Commit calendar for user's detail page

Working as of now. API might be have been done a bit smarter.

I'm using svg and [d3](https://github.com/mbostock/d3/).

## TODO
- [x] Finalize styling
- [x] Create api for fetching number of commit per day.
- [x] Make chart work with an array of day-number pairs.

## Screenshot
![functioning-calendar-screenshot](https://f.cloud.github.com/assets/132421/681151/a50c45ba-d9a9-11e2-9a7d-cc8c0231fbb7.png)