Commit calendar for user's detail page

It's a very rough proof of concept at the moment.
I'm using svg and [d3](https://github.com/mbostock/d3/).

## TODO
- [ ] Finalize styling
- [ ] Create api for fetching number of commit per day.
- [ ] Make chart work with a object of day-number pairs instead of the array.

## Screenshot
![commit-calendar-example](https://f.cloud.github.com/assets/132421/674917/74f17586-d8e5-11e2-89da-a29b1c8d6ad1.png)