Tilt sensitivity

In this PR:

Added a back button.
Added a tilt sensitivity global variable to track user sensitivity.
added visual indicator of selection on sensitivity menu.

Notes:

There is some code in here that needs refactoring, but in the interest of time will be done in a future commit.
A lot of delays here. I found myself getting kind of impatient waiting for the fade-out of the menu, then fade-in of "sensitivity", then a fade-in of the options.