Added check to make sure at least one image plane is tiled before
continuing.
Updated code to write to file all tiles for all image planes in a BigTIFF
file that contain tiles.
Updated code to process all image plane regardless of whether they are
tiled or not.
Created BigTIFFImageList, BigTIFFTileList and Tile classes and refactored
App to use them.
Put TileWriter in its own file.
Reimplemented BigTIFFImageList and BigTIFFTileList in terms of
AbstractList.