Needs PS4 controller support (DualShock 4)

[jaredlinklater]

I will be adding this from my fork soon. This will work for USB-connected DS4 controllers, with limited support for Bluetooth-connected DS4 controllers, as the input is reported differently over Bluetooth. This will only support button presses and joysticks for now - I plan to update gamecontroller.js to allows for L2/R2 pressure reporting, battery level reporting and accelerometer/gyroscope reporting soon.