Allow user to select Soundtouch or Rubberband
Clean up keylock preference code based on review notes.
Fix use of volatile
Merge pull request #236 from ywwg/keylock-configure

Allow user to select Soundtouch or Rubberband
No spaces around ``/`` in labels as per db405827b8130f788be7146be3c3192b99254514
In Soundhardware preference, move Keylock option up. This groups options and informal labels together. Fix tab order.
Preferences>Waveforms: Update labels, add some tooltips and group options as discussed in https://bugs.launchpad.net/mixxx/+bug/896880