This also removes enums introduced to describe well-known parameters for Mixbus. Lookup now involves string
parsing every time, but this is not likely to be a notable cost.
The Editor continues to notify them, but via a direct call to ControlProtocolManager, not a signal.
The CP Manager calls the ControlProtocol static method to set up static data structures holding
selection info for all surfaces and then notifies each surface/protocol that selection has changed.
