Editing FTEQW Controller support

Mostly undocumented for now, but very useful for [[Splitscreen_mode_in_FTEQW | splitscreen]] usage. It should recognise ANY of the 16+2 buttons+triggers of typical controllers. (Windows only)

== Random Notes ==
* Xinput with a Steamcontroller works work in FTEQW, but doesn't initialize until you press the right analog trigger. Prior to pressing the right trigger, Xinput doesn't work at all -- no output from any axes.
** the way to get it to work in FTEQW is to disable "joystick" and enable "in_xinput" in the console, to keep in mind that the left thumbstick is mapped to joyadvaxis R and U, and always remember to press the right analog trigger at least once before you play 
* This is a splitscreen thing. Controllers are only enabled once you hit a button, which avoids USB's random ordering issue. Player 1 then player 2, etc. 
** This also protects against poorly calibrated controllers that might otherwise cause your view to rotate constantly even when the user isn't trying to use them.
** Normally any button should activate it, supposedly, no idea how you're finding its only the right trigger - these are technically not even buttons, but fte simulates two extra buttons so you can bind the triggers to stuff if you want.
* Joystick and in_xinput cvars are separate and distinct, in that they use two different APIs blindly without regard for whether the device is also present in the other api... ** The earlier API supports stuff that isn't trying to mimic xbox controllers, while xinput is much more precise about what the buttons on the thing actually represents, but  there is no real way to figure out whether any single device is being reported by both APIs, nor which would be the best to use even if it was. So don't enable both the same time.