better disarm method for PS3 controller

[labreuer]

Moving the left paddle on the PS3 controller to the lower left is too imprecise to qualify as an emergency shutdown. The full range of motion is a circle, not a rectangle like typical twin sticks. So there is no tactile 'lower left'.

Therefore, I suggest that pressing any two of the three buttons, { L2, R2, X }, kills all motors (commandAllMotors(MINCOMMAND)) and sets the quad to the disarmed state (motorArmed = OFF). L2 and R2 have a lot of play (I'm guessing that the analog nature of them is useful for something more than how fast they were pressed), so we'll have to figure out a good threshold.

[eelsirhc]

All buttons have digital and analogue signals. Analogue is depth-proportional, digital is immediate.