Graphics Update

-Each floor has its own individual background image.

-The elevator has an image.

-There are 6 passenger images assigned round-robin as passengers are
generated.

-GameActivity is now a fullscreen activity, and ElevatorView takes up
all of it.

-Restricted the app to Portrait mode (it looks really funny in landscape
mode, and it's nigh-impossible to read the floor numbers when it's so
stretched out.)

-Set bitmap scaling to not filter to try to reduce muddiness on
high-resolution devices.