Toggle sneak shortcut
When using a gamepad double clicking the sneak button (on an XBox controller this is the right thumbstick button) should toggle sneak permanently on/off, whereas holding it down turns it on temporarily until the button is released. Currently only the temporary sneak behavior is implemented.
Since there is currently no feature to permanently turn sneak on for keyboards either, this seems like a good behavior for the sneak button in general.
(RM-4001 from redmine: created on 2017-08-06 by Paul McElroy, )