Improve documentation of configuring external issue trackers

There was some confusion over the deprecated `:issues_tracker_id` field. Added documentation.

Closes #1514

See merge request !580

Closes #1514

Added " How to maintain tight control over the number of active users..."

Added " How to maintain tight control over the number of active users on your GitLab installation" to documentation.

Please check that documentation is OK before accepting Merge. I took if from https://gitlab.com/gitlab-org/gitlab-ce/blob/master/config/gitlab.yml.example#L149

cc/ @sytse

See merge request !1792

Fix Error 500 when searching Wiki pages

If a Wiki page turns up a hit in the search results, an error will occur:

```
Completed 500 Internal Server Error in 836ms

NoMethodError - undefined method `slug' for "test.markdown":String:
  app/helpers/wiki_helper.rb:10:in `namespace_project_wiki_path'
  app/views/search/results/_wiki_blob.html.haml:4:in `_app_views_search_results__wiki_blob_html_haml___2752621660395393333_70299911622700'
  actionview (4.1.9) lib/action_view/template.rb:145:in `block in render'
  activesupport (4.1.9) lib/active_support/notifications.rb:161:in `instrument'
  actionview (4.1.9) lib/action_view/template.rb:339:in `instrument'
  actionview (4.1.9) lib/action_view/template.rb:143:in `render'
```

An unhandled String containing the name of the Wiki page would be provided to the URL path generator. This MR handles that case.

Closes #1547

See merge request !592

Add current_sign_in_at to api User

Unescape branch names in compare commit

The upgrade in GitLab v7.9 to Rails v4.1.9 caused all branch names in the compare commit mode to be escaped (e.g. `/` to `%2F`). The compare mode would not always work when comparing against branch names with a forward slash.

Opted to unescape the branch name rather than use a wildcard segment to prevent escaping slashes because it seems like a more sensible URL. The slashes in this case aren't really represented by a tree structure (e.g. /compare/one/two/branch..another/branch/here).

* Closes #1399
* Closes https://github.com/gitlabhq/gitlabhq/issues/9105

See merge request !582

Re-annotate models

Re-ran `annotate` to fix model annotations.

See merge request !603

Fix config template from parse errors

62aa05dd added comments that were not commented out. CI test builds do a `cp gitlab.yml.example gitlab.yml` and thus were failing.

See merge request !602

Fix file paths for installations from the source

See merge request !583

Add snippet visibilty as parameter to API doc, closes #1562

## Description

Snippet visibility level was added to API but was not to its documentation.

Related to following commit: 928fc94c

@axil Can you review?

See merge request !601

add missing word to changelog

Remove duplicate CHANGELOG line for v7.10.0

The other one is 3 lines below the removed.

[ci skip]

See merge request !563

Update config.yml.example

See merge request !597

Fix #6417: users with group permission should be able to create groups via API

Group milestones by title in the dashboard and all other issue views

add common method to force utf8 and force oauth properties to be utf8

Allow primary email to be set to an email that you've already added.

Fixes gitlab-com/support-forum#106.

When the user sets their primary email to an email that they've already added to their account, this patch makes sure that secondary email record is destroyed, and a new email record is created for the old primary email. This is based on the assumption that in this case no email was meant to be deleted, but the user simply wanted to change which of their emails is primary.

See merge request !591

Add application setting to restrict user signups to e-mail domains

This feature was requested long ago:

http://feedback.gitlab.com/forums/176466-general/suggestions/4118466-ability-to-register-only-from-ceratain-domains

This MR is based off !253 but changed to use application settings and use wildcard strings
to give more flexibility in pattern matching. Regexps seemed overkill and prone to mistakes.

Also note that validation is ONLY done on creation to prevent breaking existing users who do not have a whitelisted domain. However, this allows a user to sign-up and change his/her email to a non-whitelisted domain.

Screenshots:

![image](https://gitlab.com/gitlab-org/gitlab-ce/uploads/b312046aae03971f37f4247382971fc6/image.png)

![image](https://gitlab.com/gitlab-org/gitlab-ce/uploads/94bdf3ffaf37c2e8324eff83308f81f0/image.png)

See merge request !598

Don't delete gitlab-test-fork folder after every test run

72a7febe added a forked repository cloned to `tmp/tests/gitlab-test-fork` but because it wasn't added to the list of folders not to delete every run, it was being cloned every run and adding extraneous console output.

See merge request !600

Make Reply-To config apply to change e-mail confirmation and other notifications sent through Devise

Notifications sent through Devise were using the default From: address, and due to a broken test line nothing was actually being run.

The only way to customize the Devise Reply-To field is to use a custom mailer. Moved the e-mail configuration out of the initializers to accommodate this.

Closes #1556

See merge request !596

This feature was requested long ago:

http://feedback.gitlab.com/forums/176466-general/suggestions/4118466-ability-to-register-only-from-ceratain-domains

This MR is based off !253 but changed to use application settings and use wildcard strings
to give more flexibility in pattern matching. Regexps seemed overkill and easy to get wrong.

Only restrict e-mail addresses upon creation

Add a page title to every page.

![You get a title, and you get a title; everyone gets a title!](https://i.imgflip.com/kvmq8.jpg)

The `page_title` helper pushes the provided string at the end of the title, but because of the order that layouts are rendered in by ActionView, the result is always this:

```
<title from view> |
<title from as specified in the controller or by its layout> |
<title from layouts/_head>
```

For example: `Merge Requests | GitLab.org / Gitlab Community Edition | GitLab`.

All a developer needs to know is to put a `page_title` call describing the page in question at the start of every template.

To get everything where I wanted it to go without too much duplication, I had to make some changes around layouts, sidebars and controllers.

See merge request !593