Add a contributions calendar to user profiles showing commits

No tests yet, and still under progress but we need comments and feedback

Screenshot where there are no commits:
![u4bfaft](https://cloud.githubusercontent.com/assets/6151901/2940328/4e65c6f4-d97c-11e3-9423-d03d1420c766.png)

When a user has commits:
![n753upy](https://cloud.githubusercontent.com/assets/6151901/2940329/4f660b72-d97c-11e3-8c00-d37ecccf7b96.png)
It will show a calendar covering a timeframe from the year before up to his latest commit.