Improved interactive development

[Kevinpgalligan]

Things to add:

• (Gleefre's suggestion) Have a slot/option like :restart-on-redefinition nil, so the window doesn't have to restart every time the defsketch is recompiled. If someone is just tweaking the drawing code, for example, or how the state gets updated (as opposed to adding new state), then they may not need to restart the window. Or even if they're adding new state, maybe they don't need to refresh (this might require ensuring that the new draw doesn't get called before any new slots are added).
• May also want another config option to control whether the slots are reinitialised with prepare.
• A hook or hotkey (like close-on) to manually trigger restarts.

Together, these features would enable something closer to "true" interactive development.