Advertise MPD with Avahi

A rudimentary implementation to resolve #39, ignoring dbus errors (just restart), name collisions (choose a fresh name), etc.
Add genre, composer, and performer tags and use them
Merge remote-tracking branch 'upstream/develop' into feature/extra_tags
Date is not mandatory AFAICT
Merge branch 'develop' of https://github.com/mopidy/mopidy into feature/extra_tags
Fix testcases after merging mopidy/develop
Added a ton of extra tests and expanded a few to include new tags
Add missing regexp
Add frontend MPD tests for 'search comment "foo"'
Avahi python compatibility fix
Avahi wrapper moved to utils
Avahi constants named
Avahi hostname choice extracted for reuse
core: Letting filter() accept lists
Adding a 'to list' conversion and correcting horrible mistake in comparison (put it reverse)
Advertise HTTP with Avahi
Add more tests
Adding test case
tests: Fixing self confusion mistake
docs: Documenting tracklist's new filter() feature
core: Changing input to accept also sets, as might be also used.