Add real favicon

I tend to leave Uchiwa open in a sea of other tabs, and I always lose it. This adds a U as the favicon

![screen shot 2014-10-08 at 1 18 37 pm](https://cloud.githubusercontent.com/assets/465717/4558903/6251d156-4ee5-11e4-8fb2-446a76c6e1e1.png)