Backport premailer and diff changes from EE

Backport part of https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/151

See merge request !3318

Upgrade Rubocop from 0.35.1 to 0.38.0

See [Rubocop's Releases page](https://github.com/bbatsov/rubocop/releases) for more info on what changed.

Descriptions/StyleGuides removed as discussed in #14233.

Changes:
- Enable DisplayCopNames for lint output.
- Default behavior for `Alias` changed, set to enforce `prefer_alias_method`.
- Enabling Rails cops changed to new syntax.
- Remove StyleGuides and move Descriptions to comments.
- Add missing cops.
- Add TODOs for cops that should be enabled in the future.
- Set TargetRubyVersion to 2.1.

See merge request !3197

Discussed in #14233.

See [their releases](https://github.com/bbatsov/rubocop/releases) for
more info.

Changes:
- Enable DisplayCopNames for lint output.
- Default behavior for `Alias` changed, set to enforce `prefer_alias_method`.
- Enabling Rails cops changed to new syntax.
- Remove StyleGuides and move Descriptions to comments.
- Add missing cops.
- Add TODOs for cops that should be enabled in the future.
- Set TargetRubyVersion to 2.1.

Fix a few remaining uses of `0px`.

See #14299 for more information.

cc: @jschatz1 

See merge request !3310

Make HTTP(s) label consistent on clone bar

Sites that use http:// for the external_url should always display HTTP on
the clone bar. Similarly, sites that use https:// should show HTTPS.

Currently, the inconsistency looks like:

![http-magic](/uploads/945fda580f7ba5aee36cc572b49baf2b/http-magic.gif)

Also restores the tooltips that vanished in 7ba4482f:

![image](/uploads/b5a7b3e68b4992a447fcaa51915e866c/image.png)


See merge request !3319

Fix spacing below edit note form

Also changed to allow the CSS to decide what should be hidden when editing

Thanks @JobV for having eagle eyes 😜 

See merge request !3306

Expand the issuable sidebar when coming back from the Changes tab

Unless the user explicitly requested the collapsed sidebar.

Fixes: #14353

See merge request !3256

Fixed issue with filtered data persisting when dropdown closed

![labels](/uploads/4b9c902add76263d8488cc34ef49f142/labels.gif)

Closes #14401

See merge request !3302

Sites that use http:// for the external_url should always display HTTP on
the clone bar. Similarly, sites that use https:// should show HTTPS.

Fix bug where wrong commit ID was being used in a merge request diff to show old image

Closes #3769

Closes #14327

See merge request !3300

Closes #3769

Closes #14327

Easily (un)mark merge request as WIP using link

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/3768 and https://gitlab.com/gitlab-org/gitlab-ce/issues/3516

## Link to add `WIP` prefix (underline is visible because of hover)
![wipless_title](/uploads/72a6f7119ba9d8043ca8329641e97c3b/wipless_title.png)

## Link to remove `WIP` prefix
![wip_title](/uploads/8620ad65da9ef620b180603520fead55/wip_title.png)

## System note after WIP is added
![wip_sysnote](/uploads/2de073b75e854d2c9e243eb8b5d5c259/wip_sysnote.png)

## Widget with link to remove WIP
![wip_widget](/uploads/cf83ea93743c4c26d9df759c17cb9d7b/wip_widget.png)

## Flash after WIP is removed
![wip_flash](/uploads/27b7240cd5d7ceeb8b7b477abd94d7ff/wip_flash.png)

## System note after WIP is removed
![wipless_sysnote](/uploads/c0d3368abdf21a2f253532a9a9594d90/wipless_sysnote.png)

## Widget when current user cannot remove the WIP prefix
![wip_widget_unauthorized](/uploads/174ccf1674be86dc81c3078fe297acb7/wip_widget_unauthorized.png)

cc @creamzy 

See merge request !3006

# Conflicts:
#	Gemfile.lock

attempting to fix omniauth problem

Attempt to fix https://gitlab.com/gitlab-org/gitlab-ce/issues/3361

See merge request !2876

Add label description in tooltip to labels in issue index and sidebar

The tooltip can get quite big, but it’s so useful to inform people about what these labels mean
new

![Screen_Shot_2016-03-08_at_11.48.28](/uploads/894baaaa1f789c3a2069a924d541e64b/Screen_Shot_2016-03-08_at_11.48.28.png)

![Screen_Shot_2016-03-08_at_11.48.20](/uploads/efe4fa0960054c4071b8f6bf83024403/Screen_Shot_2016-03-08_at_11.48.20.png)

@JobV writes on Slack:
> yeah I think it’s better than not, but I’d have to try it 😃 
> 
> cautious yes, revert if it’s annoying 😉

See merge request !3124

#to_branch_name now uses the iid as postfix

Given the branch name 'mep-mep' with an iid being 1,
the current way, master's way, would yield a branch name of
1-mep-mep. The problem for larger projects however would be that
a developer might forget what iid the issue was.

When this developer would try to tab complete it would:
- Or result in 20+ branches possibly
- Or start with the wrong digit, try again with digit++
  - Would see 20 branches, repeat

Thus the obvious way of solving this is letting the dev tab complete
on the issue title, which is easier to remember.

@DouweM Should this be labelled `pick-in-master`? 

See merge request !3308

Add information about `image` and `services` field at `job` level in the `.gitlab-ci.yml` documentation

Fixes #14366

/cc @tmaczukin @ayufan @axil

See merge request !3277

Dedupe labels in labels selector in Dashboard pages

Fixes #14418.

See merge request !3311

Also moved useless helper methods and directly to the
DashboardController.

See #14299 for more information.

[ci skip]

Do not retry "git gc"

To prevent 'git gc' timing out on a large repo and then bouncing
around in the retry queue.

See merge request !3266

Fix an issue when the target branch of a MR had been deleted

Before displaying the "diverged commits" note, we're checking if the MR
is open, but we should check if it's mergeable instead because this
check ensure the source and target branches exist.

This was introduced by !2217 and fixes #14388.

See merge request !3294

Refactor colors and lists

* Introduce 2 color links: black and blue
* Use black color link for UI elements like lists
* Refactor lists to use .title nested under li
* Make all lists (events, todos, activity, projects etc) use style
* List colorschema is now 333 for links and 555 for text
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

cc @jschatz1 @skyruler 

See merge request !3307

Given the branch name 'mep-mep' with an iid being 1,
the current way, master's way, would yield a branch name of
1-mep-mep. The problem for larger projects however would be that
a developer might forget what iid the issue was.

When this developer would try to tab complete it would:
- Or result in 20+ branches possibly
- Or start with the wrong digit, try again with digit++
  - Would see 20 branches, repeat

Thus the obvious way of solving this is letting the dev tab complete
on the issue title, which is easier to remember.

* Introduce 2 color links: black and blue
* Use black color link for UI elements like lists
* Refactor lists to use .title nested under li
* Make all lists (events, todos, activity, projects etc) use style
* List colorschema is now 333 for links and 555 for text
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

We have to ensure source_sha and target_sha are not nil before calling
Gitlab::Git::Commit.between.

Before displaying the "diverged commits" note, we're checking if the MR
is open, but we should check if it's mergeable instead because this
check ensure the source and target branches exist.

This was introduced by !2217 and fixes #14388.

Add avatar to issue and MR pages header

closes #14395
# For Issues

### Before
![Screen_Shot_2016-03-18_at_4.27.25_PM](/uploads/b097c8e304c9737e2f46ee25667829bf/Screen_Shot_2016-03-18_at_4.27.25_PM.png)

### After
![Screen_Shot_2016-03-18_at_4.22.10_PM](/uploads/f7d2b12c9455950c2e660b33e27c1827/Screen_Shot_2016-03-18_at_4.22.10_PM.png)

# For Merge Request

### Before
![Screen_Shot_2016-03-18_at_4.27.09_PM](/uploads/50c7b6ee346f749f448647004ae6031b/Screen_Shot_2016-03-18_at_4.27.09_PM.png)

### After
![Screen_Shot_2016-03-18_at_4.24.17_PM](/uploads/abd37ccf030e0b6d10521a6937206de6/Screen_Shot_2016-03-18_at_4.24.17_PM.png)

See merge request !3301

Refactor variables

Fixes #13803 and other color inconsistency across application

cc @jschatz1 @skyruler 

See merge request !3304

Also changed to allow the CSS to decide what should be hidden when editting