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.
When the backend is dropped or changed, on engine-restart
the connection_handler() re-establishes already connected ports.
There's no disconnect when the backend dies or is hard-stopped.
* make shift buttons equivalent
* 2 x stop: move to session-start
* RTZ: return to zero (not session-start)
* in Pan mode: encoder controls pan-width (w/o shift)
