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.
This should check the current value of inputSensitivity (or maybe it should be stored as one of high, medium, low?) and make the relevant option big accordingly. If I set it to high and then go back into options, medium will always appear selected first.