Improve XOColor fallback logic

We was failing if the value in gconf was None. Also parsing
the string once just to see if it's valid was pretty dumb.
Merge pull request #16 from dnarvaez/xocolor

Improve XOColor fallback logic
Add API to close an html activity

We are exposing it using a websocket server. The port of the server
is passed in the search string of the file:// url.
Require authentication before making API calls

Otherwise anything might access the bus.

Note: This will not work if the user moves to another html page.  They
will not have a port/key passed in the query string of the URL, so
they won't be able to connect.
Add a get_xo_color API