Surge++ Knobs

[baconpaul]

We have a very crude knob in Surge++ now which is swappable in, and an interface it begins to support, but it is incomplete in almost every way.

Along with #1362 we what to make sure the features and parameters for the knob are reasonable.

I think, following the surge-rack approach, we want a 3 layer SVG knob. So a rotating background, a shadow, and a rotating pointer foreground. But we also have to support modulation so some real design here.

I guess the first thing here is: What would a good example of a knob with modulation be and how would we parameterize it?

[baconpaul]

Re-tooling the S++ plan so closing these issues.