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.  

Good ... `table['something']` should be a `Column` object, but behavie like an array, I think.
(I didn't try this locally yet ... I only saw a test failure in an old travis-ci log.)