Support other joysticks/button mappings

[nstiurca]

Unfortunately, joystick_teleop_node is almost unusable with a PS4 controller because axis 3 maps to the left trigger. Also, the emergency stop button maps to X on PS4 controller, although from the comments it seems like it should map to O which is generally PS4's equivalent to Xbox's B button.

I can implement this quickly and easily with an additional ~mapping parameter or such, defaulting to "xbox", but would also accept "ps4".

[nstiurca]

Question: what exactly does axis 3 map to on Xbox controller? I would guess left thumb stick side-to-side? I could also see it being right thumb side-to-side.

[nstiurca]

(axis 3 is currently used for turning if you can't be bothered to read the source)