Added url blacklist to settings panel

Uses modified code from the Vimium plugin. I had to write it using commas as separators since we only get a one line text box for Safari extensions. It does support * as wildcards.

The input box is a bit small on my screen, so I suggest dropping the "(blank for none)" part of the first setting's title:
![screen shot 2013-11-07 at 5 25 13 pm](https://f.cloud.github.com/assets/157232/1496498/d1101aea-47fb-11e3-91ac-4103ea3ed452.png)

We could include that information in the readme file instead.