Minor design change grab-bag 🎉

I started with one simple change and found a few more, so here they are.

### Simplify icon style selectors

All FontAwesome icons have an `fa` class, so just use that.

### Don't override color of code blocks in notes

This was a pet peeve of mine.

| Before | After |
|:------:|:-----:|
| ![Screen_Shot_2015-04-23_at_4.14.23_PM](https://gitlab.com/gitlab-org/gitlab-ce/uploads/c77cb0816bf0f05cb8c4105cdd8b3ec6/Screen_Shot_2015-04-23_at_4.14.23_PM.png) | ![Screen_Shot_2015-04-23_at_4.15.44_PM](https://gitlab.com/gitlab-org/gitlab-ce/uploads/463c1d2052e12444563f5e2c102ac51e/Screen_Shot_2015-04-23_at_4.15.44_PM.png) |

### Items with tooltips don't need a 'data-original-title' attribute

This attribute gets added dynamically by Bootstrap's tooltip JS based on the `title` attribute

### Fix Profile > Design live-updating

`ui_blue` wasn't added to the list of classes to remove, so if a user changed to that theme, any subsequent changes wouldn't be live-updated.

This change refactors Gitlab::Theme a bit to make it harder for this to happen in the future with new themes.

### Remove the `has_bottom_tooltip` class

Bootstrap's tooltip JS can read the placement from a `data-placement` attribute.

Further, when we supply the `selector` option to `tooltip`, tooltips will be added to any dynamically-added elements matching the selector, without us having to re-call the `tooltip` method.

See merge request !569

[ci skip]

Refactor ReferenceExtractor

See merge request !557

When collapsed it's on the right like everything else, when expanded
it's on the bottom.

Also matches CommitReferenceFilter's new behavior of always using short
SHAs in the link text.

Now when a user pastes a full SHA like
`d7f61aff`, its link text will only show
`d7f61aff` for brevity.

Bootstrap's tooltip JS can read the placement from a `data-placement`
attribute.

Further, when we supply the `selector` option to `tooltip`, tooltips
will be added to any dynamically-added elements matching the selector,
without us having to re-call the `tooltip` method.

`ui_blue` wasn't added to the list of classes to remove, so if a user
changed to that theme, any subsequent changes wouldn't be live-updated.

This change refactors Gitlab::Theme a bit to make it harder for this to
happen in the future with new themes.

Bootstrap's tooltip JS just uses the `title` attribute.

All FontAwesome icons have an `fa` class, so just use that.

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