Add "reinitialize joystick" option

[jwbrase]

There has been a longstanding bug on Linux that if any joystick axis is off-center when the game is started (most commonly the throttle because everything else tends to be springloaded to center itself), that axis will be biased off-center and will not have its full range of motion until the game is restarted. The purpose of this thread is not to bring the bug to the devs' attention (I'm fairly certain it's already known), or to advocate that it be fixed more quickly, it is simply to suggest a possible workaround should a fix be technically unfeasible (assuming that the workaround isn't unfeasible for the same reasons as the fix) or lower priority than other bugfixes.

My idea is basically to add a button on some options screen, or maybe a keybinding, that causes the game to reinitialize its joystick code. Assuming that the user has centered all axes, this would then cause the joystick to behave correctly without necessitating a full restart (the caveat being that if the reinitialization button were pressed with the joystick off-center, it would then cause the joystick to misbehave).