Rename operator interfaces

[appsforartists]

At some point, we had a convention that interfaces should end with able; hence, all the operator interfaces, e.g. MotionMemorable. That convention hasn't really held true - both MotionObservable and the interactions are examples of concrete classes that end in able.

Thus, we should clean up the interfaces to better distinguish them. The winning proposal so far is to capitalize the operator name, e.g.:

withPluck(): S & Pluck {
  return class extends superclass implements Pluck {
    pluck() // ...

withRemember(): S & _Remember {
  return class extends superclass implements _Remember {
    _remember() // ...

[appsforartists]

Another option is to rename the interactions to avoid the able suffix. That should probably happen too, since most compound interactions won't lend themselves easily to "$VERBable" names.