Paint or cross strokes by holding down mouse button

[Braisa]

[Braisa]

The current functionality still requires polish; it is laggy and doesn't work as desires for crossing strokes. Since crossing and un-crossing uses the same keybind, holding down the cross button on the same cell will constantly cross it and un-cross it. Ideally, the input handler should detect when the cross button is released until it allows to swap between crossing and un-crossing. This is, within the same button press, only one of either crossing or un-crossing should be allowed, depending on if the initial cell pressed was blank or already crossed respectively.