Added future_with_result utility...

This is kind of like defer.succeed(value) from Twisted-land.
Augmented SqlRepresentableType to list unique column entries and...

also to return random data.
Added convenience methods to library for accessing track inforamtion...

Not currently unit tested, as I found to my detriment when trying to plug
everything together just now! Committing because I think they work, need
to go back to improve coverage though. Boo for non-TDD.
Added Queue class, ancilliary stuff and tests...

The Queue class is actually quite smart - it combines auto-generating
modes of track listing with specific tracks queued by the user. This means
that a Queue.next() is actually a coroutine though, because we may have to
go off to the database and grab some track data. That makes testing a bit
of a pain :-( Can't think how to make it nicer right now, and also don't
like the asymmetry between next (unknown, so coroutine) and previous (just
jump back in the list, so regular callable).
Add Queue to main pyamp file...

And keybindings for next and previous track functions.
Merge pull request #16 from ch3pjw/play_queue

Added a play queue that can handle user and dynamic track listings