Allow menu control with game keybindings

[runer112]

For any key not bound to a TI-Boy CE menu control but bound to a game control, it would be nice if it also performed the menu control that logically corresponds to the game control. With the default game controls, this primarily means being able to use alpha for the same purpose as clear, which my brain always wants to do after playing for a while with 2nd generally meaning "select" and alpha generally meaning "back". But it should generally be able to work for any set of game keybindings (that doesn't conflict with the menu keybindings).

Note that it's probably important for the menu keybindings to take priority so a user with weird game keybindings can't find themself stuck in the menu.

It's pretty obvious how to map the arrows, A, and B. Not really sure how/if to map Start and Select.