Pitch scale

This is the fist chunk of commits, that fixes the scale jump issue of the pitch knob. 
https://bugs.launchpad.net/mixxx/+bug/1258617
The code is still a bit ugly because it still uses the old pitch adjust CO internally but it works. 
I am working on a solution where we just pass pitch and tempo to the scalers, which will clean up the code.
oh you're right, it's inherited from engine control, so it should be fine.

Can you add a test to confirm that the same decks are picked in the following case: with two decks, one of which has SYNC_ENABLED, the key should sync to the deck with SYNC_ENABLED.  I think that case is not handled right now.