Refactor/adapt to yosemite

I've added a new tab style that conforms with the new look in Yosemite.

I was wondering what you guys think of it so far?

### On my todo list so far:
- [ ] Change the "New Tab" icon on the right side
- [ ] Change font color depending on tab state


![screen shot 2014-09-11 at 18 51 45](https://cloud.githubusercontent.com/assets/57446/4238185/8a204502-39d5-11e4-8d96-3029bfebe997.PNG)