Current threaded debugger work

Switch status flags from int to DbgStateFlags
Make all of the * -> controller interaction use queued connections
Make public functions in the controller threadsafe
Add a new thread subclass which creates a controller and runs the event loop
Refactoring:
- status messages now created in the plugin by listening for status changed signals
- controller now responsible for starting the debugger when it's not running
- move shell logic to controller

Still todo:
- callbacks likely broken or using the wrong thread (haven't figured out where they are called yet)
- need to make the controller more forgiving of being busy, so that you can eg. step twice without waiting for the first step to complete (yay :)
- regression fixing, for sure