* how long can UI signal callbacks take to execute? What happens if they block?
  where ENSURE_CORRECT_THREAD is a macro that is modelled on ENSURE_GUI_THREAD
  if the handler is not called in the "correct thread", it will use a pseudo-RT-safe-enough technique to get the correct thread to recall "handler" later on, and return.

* jog with transport rolling doesn't work properly. My use of ScrollTimeline also doesn't work.
* make sure rew button can go past the previous if pressed twice, relatively quickly.
* finish button mapping.
* concurrency for bank switching? And make sure "old" events aren't sent to "new" faders
* TODOs in code
* removal of a route results in a strip that isn't dead, but doesn't have any effect on the session
* use i18n. see string_compose
* docs in manual, including button assignment diagram

Later
-----
* remove commented couts
* Queueing of writes?
* Generic surface code to common location
* bulk remote id changes cause too many surface updates
* which bank switching - overlap or dead faders? Option?
* signals for buttons?
* MackieControlProtocol in namespace Mackie?
* power-cycling of surface. fd_midiport doesn't close.
* mix busses and/or a "bus-only" bank/mode
* what about surfaces like Mackie C4 and BCR2000?

Need UI integration
-------------------
* Some indication on the UI of currently bank-switched-in routes?
  Useful for surfaces that don't have a scribble strip.
* use current zoom setting and snap state for shuttle wheel

Actual Mackie
-------------
* docs claim that unit will send a host query on init.
* test Mackie surface object. Apparently led rings don't work. Stereo busses?
* timecode & 55 char displays
* midi bandwidth

Bugs
----

* get_state isn't called on deactivate. Huh? What did I mean here?
* routes "forget" their remote_id between session save and the next session load
* definitely something wrong with remote_id assignment on session create
  (master strip assigned 0).
* editor window doesn't update route remote_control_id when it's updated in mixer window.