Renamed `Query` to `Signal` on both sides of connection so that it can be a more general concept. Added and fixed some functions of `comm.py`.
Made `comm` protocol definition checks happen at compile time, not run-time, and deleted one of these checks.
Finished renaming `query` to `signal`.
Removed the rover's RX ISR handler, since it would be called for every byte that
 comes across the bluetooth serial.