TODO

* = done, - = not done

*- add control to value
    - ideally it would be possible to either select an existing
      control, or add a control and select that. I suspect the flow
      for this inside the UI would be messy. Or not? Just push the
      control edit screen?
- log mode on ctors?









UI code rejig:
* three threads
    - jack thread, sends mon msgs to ui thread
    - ui nonblocking thread, shows monitor data and performs
      non-blocking input calls which *look* blocking from the other
      thread
    - "blocking" ui thread, which handles menu flow and has blocking
      calls, which wait for data from the other ui thread.
      
      
* classes
    - each screen has a display() method, which is called from the
      non-blocking thread with a monitor data structure.
    - each screen also has a run() method, which does actual flow
      within the screen ui, and on exit transfers to another screen.
    
* data flow
    rings:
    * jack thread -> ui non-blocking thread  
    * ui blocking thread -> jack thread
    strings and keypresses:
        ui non-blocking thread -> ui blocking thread
        (this may require condition variables)
    mode commands (e.g. "edit a string, please")
        - ui-b thread locks mutex, edits an input request structure,
          unlocks the mutex and waits on a condition
        - ui-nb thread responds (running the appropriate editor or
          just keypress input) and when ready, fills in the response
          and signals the condition
        - ui-b thread continues.