WIP: Aper adding wcs and support for various input data

Adding non-pixel coordinate support to ``aperture_photometry``.  Depends on #107.
(discussed in the telecon already, but this is just a reminder)
Should also accept `ImageHDU`, and use the main user-facing class: e.g. ``isinstance(data, (fits.PrimaryHDU, fits.ImageHDU))``