Saving state, stage 2

[p0nce]

Follow-up from #352

The goal is to save/restore any extra state that allows to render audio, not necessarily global UI settings (somehow best handled with a VFS abstraction and config files I think).

• Find a binary-serializable, nestable, thread-safe, with key-values, suitable for large blocks of data.
  • Probably take an existing data format like CBOR, BJSON, etc. Something with 1:1 human readable version would help. Not Turtle lol. A DOM but for data.
  • A big point is to handle the bidirectional communcation for UI and DSP. Same problems as Parameter, who lacked two interfaces for each view. Probably we need an algorithm of tree merging?
  • Typical Java UI library have listener that listens to generic Event. This is useful when we don't know yet that there will be a button widget with an onButtonClick event. See also Javascript solutions. If we do State V2, ideally it should be able to replace any such listener. Mouse, keyboard, and params would be branches of the tree.
• Make such variant values have Listener of their own, callback on add/remove, things like that