Add Trac Support

Add support for Edgewall Trac. Tested in versions 0.12 - 1.1.2dev of
Trac. Custom styles added for Trac v0.x, Trac v1.x, and WordPress Trac.
For now, supported domains are trac.edgewall.org, trac-hacks.org,
trac.wordpress.org, and bugs.jquery.org. We may want to add to this list
in the future or allow users to add their own custom domains in
extension options.