Support referencing issues to a project whose name starts with a digit

Gitlab supports adding users or projects whose name starts with a "_" or a digit, but the regexp in markdown.rb enforces "a-zA-Z" for the first character.

This change allows to reference issues or merge requests in other projects whose name starts with a digit, like `owner/2ndtestproject#123` or `2nduser/superproject!123`.

See merge request !264

Fix protected branches routing

### Summary

On the master branch, if you attempt to access the protected branches in the project settings with an empty repo, you get `NoMethodError - undefined method "project_url"`.

### Steps to reproduce

1. Check out GitLab master and run.
2. Create a new project.
3. Go to Settings.
4. Click on "Protected branches"

### Expected behavior

The controller is supposed to redirect back to the projects page since there are no branches.

### Observed behavior

Internal Error 500

### Relevant logs

```
NoMethodError - undefined method `project_url' for #<Projects::ProtectedBranchesController:0x007fd920054af0>:
  app/controllers/application_controller.rb:157:in `method_missing'
  actionpack (4.1.9) lib/action_dispatch/routing/polymorphic_routes.rb:142:in `polymorphic_url'
  actionpack (4.1.9) lib/action_dispatch/routing/url_for.rb:161:in `url_for'
  actionpack (4.1.9) lib/action_controller/metal/redirecting.rb:91:in `_compute_redirect_to_location'
  turbolinks (2.0.0) lib/turbolinks.rb:15:in `_compute_redirect_to_location_with_xhr_referer'
  actionpack (4.1.9) lib/action_controller/metal/redirecting.rb:71:in `redirect_to
```

### Fix

I added a unit test for the empty project case and replicated the issue. I added the URL router helpers that appear to be necessary after 42387b73.

See merge request !359

[bugfix] Merge request diff view behaviour fix

More reasons why prefixing is good

Inspired by http://www.dwheeler.com/essays/filenames-in-shell.html

See merge request !1604

Add comment about note attachment redirect.

See merge request !1612

New Issue Header

Fixes #2073

- I've switched it from "New Issue" to "Create Issue". Small change, but grammatically correct.

See merge request !1611

This is what’s actually allowed when creating a user or a project in gitlab.

Error in docs for closing an issue

API docs for issues says you set parameter 'closed' to '1'.  I was not able to do that but I could set 'state_event' to 'close' which closed the issue.

Does not work
"https://gitlab.com/api/v3/projects/:id/issues/:issue_id?closed=1"

Does work
"https://gitlab.com/api/v3/projects/:id/issues/:issue_id?state_event=close"

See merge request !342

Expose avatar_url in projects API

* Impl Project#avatar_url
* Refactor ApplicationHelper: Use Project#avatar_url
* Update changelog

formatting cleanup on mysql_to_postgresql.md

use gitlab branch of mysql-postgresql-converter

Correct json payload [ci skip]

Update version sorter to 2.0.0, fixes #8572

Fix typo

Mention audit events ee feature in logs documentation.

Related to gitlab/gitlabhq#1979

See merge request !1609

Add 'confirm' option to users api

For #1990

Based on https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/129

See merge request !1610

Conflicts:
	lib/api/users.rb

Remove CI sections related to release tool, update steps in monthly and patch release documentation.

See merge request !1608

Remove CI sections related to release tool, update steps in monthly and patch release documentation.

Update project_milestone_path update route.

See merge request !1605

Redirect old note attachment path to new uploads path.

See https://gitlab.com/gitlab-org/gitlab-ce/commit/0d884ff2b1beae085050fe6729bd88783891fc71#note_891797

See merge request !1607

Fix and test user contributed projects.

Fixes #2077.

See merge request !1606

Include number of affected people in all/group mention autocomplete item.

As mentioned in #2054.

To minimize misuse of all/group mentions, the autocomplete title includes the number of members this mention will notify, so users will be more considerate what groups they mention.

Example:

at-all "**all** All Project and Group Members (12)"

at-gitlab "**gitlab** GitLab (12)"

See merge request !1596

Introduce shortcuts for routing helpers

See merge request !1600

Filter icons look like proper buttons

The filter icons (Push events, Merge events, Comments, Team) now have a border
that signifies they can be pushed. This not only keeps it in line with the rest
of the application buttons, but it makes it more obvious, especially for the
Merge events button with a checkbox icon.

Fixes #1993

See merge request !1576

Fixes grammatical consistency and small changes

This commit adds consistency to small things like periods, commas,
and gives additional information to buttons and headers, etc.

Fixes #2002, #2005, #2003.

See merge request !1570