Factor functionality out into handler classes

Add MediaKeysHandler, NotificationsHandler and TelepathyHandler
Move self.spotify to MediaKeysHandler
Remove unused SpotifyPlayer
Implement Telepathy.shutdown
Pass handlers to SpotifyGnome in an array
Handlers inherit from abstract Handler class
No need for global ENABLE_* variables
Ego massaging
Add CurrentSongHandler

Factor out updating the current song into CurrentSongHandler, and mixin to NotificationsHandler and TelepathyHandler.
Fix typo
Merge pull request #11 from mattjbray/refactor

Refactor features into multiple Handler objects for cleaner separation of concerns.