Make stop button in same screen location as play button

[ductape]

As user of the rovercode app, when I press the play button, I commonly turn my head to watch my rover. When I want to stop execution, I have to look back to the screen to navigate my mouse to the stop button as the stop button is at a different screen location to the play button. It would be very convenient if the stop and play button were always overlapping even though they aren't shown at the same time so that I could just click again to stop when not looking at my screen.

BONUS: support a keyboard shortcut for play/pause/stop like IDE/Debuggers, e.g. F8 (or preferrably something more convenient for laptops since function keys are commonly defaulted to audio controls instead of functions without needing the FN key.

[cabarnes]

The first part has been addressed in #192