Polyrhythmic/polimetric metronome

Polyrhythms like in those trainers https://play.google.com/store/apps/details?id=com.autumnrockdev.polyrhythm and http://namarikarte.com/polylylyrhythm/ are pretty much useful. Different meters could be marked as light/medium/powerful vibration, so 3 simultaneous meters could be held.

Merged into "App & wearables: Polyrhythm support" #158