Resolve "Clean up CSS for project alerts and flash notifications."

## What does this MR do?

Cleans up CSS and html for alert stripes at the top of project pages.

## Screenshots

#### Before:

![Screen_Shot_2016-12-16_at_2.39.01_PM_copy](/uploads/6a700cf1e41557c00cdaef40f6a2a5b2/Screen_Shot_2016-12-16_at_2.39.01_PM_copy.png)

#### After:

![Screen_Shot_2016-12-16_at_2.39.23_PM_copy](/uploads/c849578becc3a634e8b15ab5340d86a2/Screen_Shot_2016-12-16_at_2.39.23_PM_copy.png)

## Are there points in the code the reviewer needs to double check?

In order to get multiple alerts to appear manually while testing, I simply added the following block to [app/views/shared/_no_password.html.haml](app/views/shared/_no_password.html.haml):

```

.no-password-message.alert.alert-warning.hidden-xs
  You won't be able to pull or push project code via #{gitlab_config.protocol.upcase} until you #{link_to 'set a password', edit_profile_password_path} on your account

  .pull-right
    = link_to "Don't show again", profile_path(user: {hide_no_password: true}), method: :put
    |
    = link_to 'Remind later', '#', class: 'hide-no-password-message'

.no-password-message.alert.alert-warning.hidden-xs
  You won't be able to pull or push project code via #{gitlab_config.protocol.upcase} until you #{link_to 'set a password', edit_profile_password_path} on your account

  .pull-right
    = link_to "Don't show again", profile_path(user: {hide_no_password: true}), method: :put
    |
    = link_to 'Remind later', '#', class: 'hide-no-password-message'

.no-password-message.alert.alert-warning.hidden-xs
  You won't be able to pull or push project code via #{gitlab_config.protocol.upcase} until you #{link_to 'set a password', edit_profile_password_path} on your account

  .pull-right
    = link_to "Don't show again", profile_path(user: {hide_no_password: true}), method: :put
    |
    = link_to 'Remind later', '#', class: 'hide-no-password-message'
```


## Why was this MR needed?

More alert-warning stripes are coming via the CI usage limits implementation in EE (https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/965), and these layout margins and colors were becoming messy.

## Does this MR meet the acceptance criteria?

- [x] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added
- [ ] ~~[Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- [ ] ~~API support added~~
- Tests
  - [ ] ~~Added for this feature/bug~~
  - [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?

Closes #25743

See merge request !8151