Initial import

Chrome extension to put a big ass warning thingy on certain pages so I
don't accidentally start reading them.

Has all the relevant functionality (though it looks quite shite):
    - configure domains through options page
    - sync blocked domains through google cloud
    - pop up warning overlay

TODO:
    - Make stuff pretty
    - options page is limited to 10 items currently
    - putting a comment in there why a certain page is in that list
      might be useful