matter.js: piano action

:steam_locomotive: I think the [upright piano](http://codepen.io/sharethewisdom/full/RKRVrL/) action may be good
for a challenge. Also see the [grand piano](http://codepen.io/sharethewisdom/full/GrWoXb/) action.

My disorderly attempts to animate svg parts using
GSAP (see www.greensock.com), turn out being a
bit heavy on the CPU.

Thanks to the CodingTrain I got to know matter.js!
This is perfect, and I'm eager to completely rethink
my attempts. I'd like to have a physical model, and:

* render on canvas (GPU)
* maybe move away from svg
* not hard code the collisions, velocities etc
* trigger a sound when the hammer collides with
the string until the damper mutes it
* provide parameters (sliders!) to:
- adjust screws
- bend the metal rod of the catcher
(on the back of the key lever)
- change the tension of springs

I'll post back here if I got a working attempt.
cheers! Bart

Start with the upright and grand piano CodePen examples linked in the issue, then review Matter.js documentation for the canvas, collision, sound, and slider ideas listed. The proposed behavior spans several areas and does not define acceptance criteria, so scope and a concrete definition of done would need to be agreed before coding.

Scritto dal modello di indicizzazione a partire dal testo della issue.