Reference style links with relative links in markdown

#996

```
Adds relative links support to reference style links, eg:

[GitLab API doc directory][GitLab API directory listing]

[Maintenance][Maintenance rake task]

\[GitLab API directory listing]: doc/api/
\[Maintenance rake task]: doc/raketasks/maintenance.md
```

Permissions: Developer can manage issue tracker now

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Improve merge request accepting logic

Add locked state to merge request during `accept` action.
Prevents mr being `triggered as merged` twice (hooks, emails etc)
Fixes #998 #729

Conflicts:
	spec/models/project_spec.rb

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Report success/failure of DB backup commands

Development  Project Seed Data Fix

After this commit https://dev.gitlab.org/gitlab/gitlabhq/commit/1d2bdb4d5880bb1ad39b62c81ff2971aa0cb3798 Contexts were replaced with Services. One context remained in the seed data which means development seeding will fail.

@dzaporozhets Do we want to backport this to 6.5 too?

/cc @jacobvosmaer @sytse

Ssh Docs

Oudated Version Headers

If we don't update version numbers we should not include them since they are confusing.

Release Procedure

This should be in line with what is actually happening.

Jira Integration

Check specifically for Unicorn in rack config.ru file

Assembla service: Project name was hardcoded (oops)

Don't assume that if the Rack server is not Passenger then it must be Unicorn. There are many other Rack servers in the world (uwsgi being one example that people use a lot).

The reverse check is much more logical, i.e. check explicitly for Unicorn

Enhance responsive UI for the login screen.

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Conflicts:
	features/steps/project/project_fork.rb
	features/steps/project/project_forked_merge_requests.rb
	features/steps/project/project_issue_tracker.rb
	features/steps/project/project_markdown_render.rb
	features/steps/shared/project.rb

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>