Add application type flags and an AssetManager singleton wrapper class.

The flags make it easier to determine the type of application we're running. While, the singleton wrapper is to ensure we only have one instance of an AssetManager.
Begin adding in map and physics support.
An Excel spreadsheet of Android devices. Maybe of some use, but is currently incomplete.
Modify gravity system to use only the accelerometer.

By using the compass (magnetometer) the game is limited to a smaller segment of devices. There are other issue that come with using the compass.

The accelerometer values are being used as-is, so testing will need to be done to fix noise and flipping issues.
Smooth gravity rotation to eliminate most, if not all, noise.

close #13