Fixed adding groups. Used jQuery loop.

The loop that adds the groups to the #repos must be driven by jQuery.
Removing unused code from addRepos. Fixed Headers.

Removed the code used for computing activity.

Fixed the left-to-right order of the header for recently modified
repositories.
Adapted grid size for categories.

The categories of repos are now at the top of the page in a smaller
header, as described in the mockup.
Reduce height of repo boxes.

To account for the size of the category headers.