Implemented joystick input.

I had to redo how input is done entirely, so more than one source of input can be used for game inputs.

I added new inputs, menu_decide and menu_back. Return and escape still have their reserved status, sending menu_decide and menu_back, respectively. Other keys are reserved too, like arrows, to ensure users can always reconfigure input.

scene/exit.lua

@@ -16,7 +16,7 @@ end
 function ExitScene:changeOption(rel)
 end
 
-function ExitScene:onKeyPress(e)
+function ExitScene:onInputPress(e)
 end
 
 return ExitScene