Sprite Implementation

Changed Drawable to GLDrawable to avoid confusion with the Android type.
Created sprite object for displaying images. Changed TextureBuffer to
use Bitmap object, because it provides more information and is more
convenient to use. Shader code was altered to support textures. There
are still bugs to work out, since the test sprite appears as a black
square.
I did the useless commit thing again

Don't commit changes with eclipse still open, or you have to make
useless commits like this for some reason.