Fix write_shape_stats() so that it writes without fundus input
Add reindex_faces_0to1() to convert 0-indices (Python) to 1-indices (Matlab) for all face indices.

This was necessary for the zernike Matlab-to-Python ported code.
Add ImageMath() function to use the ImageMath function in ANTS to perform operation on two volumes.
Change exclude_labels for spectra and zernike to [-1] in pipeline