Add new admin settings

Add new settings to the admin web UI for default project and snippet visibility levels.  See #2027.

### New settings:

![default_visibility_settings](https://dev.gitlab.org/gitlab/gitlabhq/uploads/bd6d296e39ea3c90ca6a5254b8eb1fef/default_visibility_settings.png)

See merge request !1795

Add new global application settings for default project and snippet
visibility levels.

Fix bug where Slack service channel was not saved in admin template settings

Consolidate allowed parameters in one place to avoid these kinds of bugs in the future.

Closes https://github.com/gitlabhq/gitlabhq/issues/9181
Closes #1501

See merge request !574

Simplify the `skip_before_action` logic for UploadsController

See merge request !547

Improve mobile UI for dashboard and project pages

Some love for mobile UI 😃

## Before
- - -
![Screenshot_2015-04-24-17-42-59](https://gitlab.com/dzaporozhets/gitlab-ce/uploads/827f9cefa477fc7f0d1b2d56e479a35c/Screenshot_2015-04-24-17-42-59.png)
![Screenshot_2015-04-24-17-27-01](https://gitlab.com/dzaporozhets/gitlab-ce/uploads/698eb90033d40ea7de9f599364a34d0e/Screenshot_2015-04-24-17-27-01.png)

## After
- - -

![Screenshot_2015-04-24-17-16-08](https://gitlab.com/dzaporozhets/gitlab-ce/uploads/7e3ad8bc18800f63a7be20ea31ccfd3b/Screenshot_2015-04-24-17-16-08.png)
![Screenshot_2015-04-24-17-39-18](https://gitlab.com/dzaporozhets/gitlab-ce/uploads/cde3379836530d95e94922ba5c200cef/Screenshot_2015-04-24-17-39-18.png)
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

See merge request !573

Consolidate allowed parameters in one place to avoid these kinds of bugs in the future.

Closes https://github.com/gitlabhq/gitlabhq/issues/9181

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

Don't allow username to end in period.

Fixes #2174 and #2249.

cc @jacobvosmaer Please review and test with the GitLab.com dump.

See merge request !1786

Add issue and merge request count for state filters.

Related to issue #2170

Changes relate to project issues and merge request pages, dashboard and group pages remain the same.

See merge request !1747

Make source code on GitLab more prominent.

See merge request !1741

This reverts commit c0116926.

This reverts commit c75c6b84.

Link cross-project cross-reference notes to correct project.

- Fixes #1431: Don't crash when an MR from a fork has a cross-reference comment from the target project on of its commits.
- Include commit comments in MR from a forked project.

To accomplish this, the Commit model needs to know about its project. Adding this attribute also simplifies a bunch of other methods that deal with a note's target, that previously had to have special logic for when it belonged to a commit.

See merge request !554

Tweak issue page a bit 

Add project activity atom feed and show atom feed buttons everywhere where applicable.

See merge request !555

Change "Sam" to "Dmitriy" in feature steps

"Sam" was too short and generic and caused invalid test failures due to finding other people with names like "Sammie" or "Samuel" unexpectedly.

See https://ci.gitlab.com/projects/1/builds/35205 and https://ci.gitlab.com/projects/1/builds/35093 as two recent examples.

See merge request !571

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