Allow any number of joysticks to be used (make `joystickIndex` and `useJoystick` obsolete)

[foxtacles]

Instead of relying on a joystickIndex and mapping that into the SDL available devices, I think we should follow the model I used for touch navigation: https://github.com/isledecomp/isle-portable/blob/master/LEGO1/lego/legoomni/src/input/legoinputmanager.cpp#L552

This queries all available input devices at runtime and applies any of their input states. It shoud allow all devices to be used as inputs, at any time, even when they are connected later (hotplugging)

[Ramen2X]

Can look into this in a couple days

[JPeisach]

While we're at this, can we also do gamepad support, I know it's a slightly larger task but it will be needed for other platforms

[AJenbo]

Should be separate tasks, gamepad will benefit from this but adding a control scheme on top bloats this task a lot.

[AJenbo]

Should be solved now that gamepad has been implemented.

[foxtacles]

@AJenbo I don't think this is solved? The code still uses joystick index: https://github.com/isledecomp/isle-portable/blob/master/LEGO1/lego/legoomni/src/input/legoinputmanager.cpp#L165

And I don't think it supports more than one input device either.

[foxtacles]

Although to be fair I guess having multiple joystick inputs doesn't make much sense here, and it seems to have a falback if the index is invalid, so I guess it's ok