multiple SDL joystick support, initial commit

Tested this with the Qt version and 2 "controllers" plugged in, works.

The SDL version still has some pad code for mobile devices in it that completely escapes me, so I don't want to touch that without hearing why it's there.

So the SDL version currently opens 2 SDL joypads with a weird configuration tailored to some mobile device while the Qt version now indiscriminately opens all SDL joypads with a configuration that seems to fit the button mapping of XBox style controllers on OSX