7.7 CE into master

```
Unmerged paths:
  (use "git add <file>..." to mark resolution)

	both modified:      app/controllers/projects/merge_requests_controller.rb
```

See merge request !293

Rescue database error

We need to check which database is setup but we cannot assume that the database exists already. Not checking this will break rake gitlab:setup for packaging as we need to do asset precompile before the database exists.

See merge request !1393

Enable signup by default

See merge request !1394

Conflicts:
	app/controllers/projects/merge_requests_controller.rb
	app/helpers/projects_helper.rb
	db/schema.rb

Doorkeeper update

https://gitlab.com/gitlab-org/omnibus-gitlab/issues/398

See merge request !1392

Update changelog

See merge request !292

Preview appearance bug

#215

See merge request !291

Gitlab shell bump

See merge request !1391

OAuth2 API documentation

https://dev.gitlab.org/gitlab/gitlabhq/issues/1713

See merge request !1388

Conflicts:
	app/helpers/projects_helper.rb

Prose requirement

Feel free to improve or link to authoritative source.

See merge request !285

Improve readme to website

addresses some of https://dev.gitlab.org/gitlab/organization/issues/100.

See merge request !1355

First entry in wiki history leads to newest revision.

Scroll below the navbar

Fixes #1866

Show the markdown anchors by scrolling below the fixed top navbar.

See merge request !1390

Git HTTP blacklist

See merge request !1328

Add Changelog Guidelines to monthly.md

Fixes #1868

Added the changelog guidelines according to the issue mentioned above. @sytse I didn't add the extra lines to the 7.7.0 log, since we have a codefreeze soon.

/cc @job

See merge request !1389