Feature: Starred groups with option to restrict view to these projects only

Added a feature for when the application has the "grouped" setting for repositories: users can select particular projects/groups that they are interested in (similar to starring a repository on GitHub) and choose to view only those repositories on the Repositories and Activity pages. Filter parameters are preserved when making changes. The user view preference is saved as a property on the user object and is therefore "sticky".

In code we have gone with the more neutral terms "selected" and "unselected", but in the UI have opted for "starred/unstarred". The current English labels for the view preference toggle are therefore `show all repositories` and `show starred projects only` while those for the buttons to select/unselect a project are: `&#9734; star` (unicode white star) and `&#9733; unstar` (unicode black star). These can of course be customized according to preference.

A Selenium test is provided.

![repositories-page-starred-groups-feature](https://f.cloud.github.com/assets/851278/166853/d49c57b8-79b7-11e2-9878-af8a8b519509.png)