Improve configuration tab's style

Hello,

This pull request is a follow-up to #312. It fixes the style of configuration tabs so that they better fit the site's design. There are several commits to ease the review process and make blaming easier:

* ed89883f: Cherry-picked from #312 ; fix the size of the tabs to address #310.

* 6d0f72bf: Update jQuery UI to 1.11.2

* 0d1b9951: Make the configuration tabs fit with the style of the site. They are styled with existing colors and styles in order to be consistent.

* faa0a957: Fix the bad displaying of configuration tabs when there's not enough content between the `.conftabs` and the left navigation ; there's a bug with left-floating elements so the content of the tab go under the navigation because the container [lose it's height](http://stackoverflow.com/a/7476799/2663959).

#### Before:

![tabs-before](https://cloud.githubusercontent.com/assets/354185/5154809/845c7e20-726e-11e4-8c0a-4cda23ac4984.png)

#### After:

![tabs-after](https://cloud.githubusercontent.com/assets/354185/5154811/87add600-726e-11e4-9790-33e1615eee54.png)

Fixes #310 and #329.

Have a nice day!
Since we are using HTML 5, this is not needed. The other ones don't have the closing slash so for the sake of consistency, let's keep it as is ; the one above has been updated. :-)