Added client list to API doc

Updating documentation to reflect #3836 (resolving #4443)

Add 'services' to path blacklist

Fix misspelling in social accounts tip

move 'make config/database.yml readable to git only' instruction

I've moved the instruction in question to the the 
'Configure GitLab DB settings'. Can't change permission to a file that doesn't already exist 😉

Editable notes

Couple of UI additions

fixed nav bar for empty repos (fixes #4375)

Adding detailed documentation of the markdown syntax.

Closes #4331

Closes #4424

This includes standard markdown as well as GitLab extended markdown as well as references to documents used.

Create uploads dir otherwise backup fails. Fix #4304

Gravatar image fixes when gravatar unavailable

Change-Id: Iad49f225f23675b843457df5d6965c7cd50e99a3

-Alt text to image was set to hash, which would make the page display hashes if the image/gravatar  wasn't available, set the alt text to '', and made the main tool bar image follow the same or similar constraints as the other images (.avatar, .s26)

Conflicts:
	app/assets/stylesheets/themes/ui_bb.scss
	app/views/snippets/_snippet.html.haml

Change-Id: I42e1e86f535486fd2556d4b3e4591f3676eea033

Rename unspecified to make it clearer and in line with scrum terminology