Add way to disable instances and devices for instances

1. **Disabling FlxControl instances, entirely:** Disabling should act as though all digital inputs are released, and all analog inputs are at 0.0
2. **Disabling keyboard/mouse/touch/gamepad for an instance:** Same effect as above, but allows you to set all players' controls to the same default mappings, but only enable keyboard on one, so that keyboard doesn't effect both players