Add beat jump support. Fixes Bug #910617.

* Works fine with master sync.
* Supports same jump lengths as beatloops.
* Added tooltips and MIDI learn descriptions.

New deck/sampler controls:
[ChannelX/SamplerX],beatjump
[ChannelX/SamplerX],beatjump_%1_forward
[ChannelX/SamplerX],beatjump_%1_backward