Consider option to create coadd image, image cube, and light curve file all into a single FITS file.

[scfleming]

Consider adding an option in gMap to create the single, deep coadd as the first extension, and image cubes as extensions 2:n. Then consider adding an option to gAperture to accept the name of a FITS file and append the gAperture light curve as a binary table instead of a separate ASCII file.

One motivation for this is creating custom loaders for an analysis UI with glue. It's not readily apparent the best solution for a custom data loader that requires multiple input files, but if the data were all in a single FITS file the custom loader can extract what's needed from it.