Added JS functions to index.html for working with Gamepads

getButtonStatuses() - takes a gamepad object and returns an array of booleans that
indicate whether or not the button corresponding to that index is pressed.

getActiveButtons() - takes a gamepad object and returns an array of integers representing
the numbers of the buttons that are pressed, starting at 1

getAxisStatuses() - takes a gamepad object and returns an array of floating point values
between -1 and 1 representing the current value of each axis

displayButtonStatuses() - prints more human-readable information regarding which buttons
are pressed to the console