favicons and styling improvements

I added favicons to the list of tabs. Now it looks like this:

![image](https://cloud.githubusercontent.com/assets/2964543/4098107/3293b0b0-2fff-11e4-9388-e0d1e84e3b4e.png)

Additionally I modified fonts and colors slightly to match them more to sublime's default scheme (Monokai).

By the way, it could be a nice feature to enable selection of a color scheme on the options page.