Add project stars.

Fix ACCEPTING MR at http://feedback.gitlab.com/forums/176466-general/suggestions/4518904-star-a-project-to-show-it-at-the-top-of-your-dashb points 1. and 2.

Before hover:

![screenshot from 2014-07-01 12 40 55 no hover](https://cloud.githubusercontent.com/assets/1429315/3442048/ca11f8be-010d-11e4-9434-327f465bfb8b.png)

On hover:

![screenshot from 2014-07-01 12 41 20 hover](https://cloud.githubusercontent.com/assets/1429315/3442051/d6bbb3e8-010d-11e4-8063-5bfa786f14d4.png)

After click:

![screenshot from 2014-07-01 12 41 53 after click](https://cloud.githubusercontent.com/assets/1429315/3442052/dea9dc1a-010d-11e4-9d5e-288e92c9fd9d.png)

Signed out:

![screenshot from 2014-07-01 12 43 23 signed out](https://cloud.githubusercontent.com/assets/1429315/3442056/e53fffc8-010d-11e4-9205-eeac7ace10a8.png)

## Implementation notes

Ignoring "Use nested module/class definitions instead of compact style." Hound warning as that style is used by all the rest of the API and recommended by Spinach itself. I propose we turn that warning off if possible.

We already have some validation messages in a locale file (https://github.com/gitlabhq/gitlabhq/blob/master/config/locales/en.yml). What do you think about putting this one there as well?