Playing around with background pages

But, I think content pages are going to be the way to go.

I'm commiting here just incase I need to rollback
Custom content for each domain

Added a new content script listing to the manifest and had it listen for
github.com
Proof of concept for github

Also playing with css.
I got rid of the font-size .8em because it showed up differently in
gmail and github.

Also, I'm trying to clean up the css.