Some fixes to how EngineVinylSoundEmu gets its speed data.

* Revert rateEngine changes I made in November to rate-limit to 10FPS.
* Don't use rateEngine anymore in EngineVinylSoundEmu (we could remove it?).
* Use speed instead of rate in EngineControl::pickSyncTarget (since rate
  includes baserate and is an internal detail of EngineBuffer).
Allow user to select Soundtouch or Rubberband
Clean up keylock preference code based on review notes.