Envelope Editor UI

[44100hertz]

Allow creating envelopes using a point-and-click UI. These will control the volume of each oscillator in the main voice -- this will be expanded.

IF Piano is complete at this point, the piano keys will act as envelope triggers. Otherwise, add a button to trigger envelopes.

The UI will consist of points separated by lines. Clicking an empty region creates a point, moving 2 points into each other merges them. A dotted vertical line indicates the sustain point -- the point at which the envelope will remain as long as the key is held. This line can be controlled by moving left and right, at which point it snaps to the nearest point.