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.
the different scaling is important for me. So for now I have changed it to:
"Pitch and keylock mode"
    *   "Offset scale, lock original key"
    *   "Absolute scale, lock current key"