Changing aperture photometry output to return astropy.table

This is the first draft for returning the photometry results in an ``astropy.table``.
I think the main question is what we want to return. Only flux, fluxerr, or something more, e.g. positions, or even the apertures (as metadata), etc.  

I'll try and catch up with all this, but I don't think we should use e.g. ``FLUX`` instead of ``flux``