Captain's Log: Stardate 77741.3

Today I finally cracked a problem that's been annoying me for a long time, where entities that have sub-types (like modulators, which can be LFOs, midi controllers, envelopes, etc) had a lot of code duplication in their GUI editors, and it was error prone to add a new sub-type. Nothing super special here, but I just finally managed to find the right abstraction that allows new sub-types to be added without it being a big spaghetti pain in the GUI code. I carried out part of the migration to the new abstraction, but there's more to do tomorrow. But it's worthwhile, because I'm about to add a bunch of new sub-types for all the new MIDI message types.