Stateful touchpad and motion sensor input generator

[dogtopus]

Develop a stateful input generator that covers the touchpad and perhaps motion sensor in the future for the planned hybrid slide mode/TGRF.

Should generate input like it was for a linear/rotary encoder. Thus should have a step left/right and (going to be and currently) end-of-the-line signaling interface.

May be used to close #12 as well.