hdf5lflib.compute_uvframe(): Make ofs_U, ofs_V default to zero
hdf-lf-utils/setCropWindow.py: New tool for configuring the cropwindow group
hdf5lflib.compute_uvframe(): Cleanup and slight rearranging of code
hdf5lflib.compute_uvframe(): Add support for cropwindow; adjust generateUVRaw