I believe that this has been completed enough to merge. Not all the functionality of the original qa_explorer is here yet (notably the visit-level exploration), but the visualizations are now up-to-date with the functionality of the new deepCoadd_obj ParquetTable dataset, and I think it's high time to get this all into master.

Also notably, the updates on this branch contain the generic PostprocessTask and MultibandPostprocessTask that enable defining functors in a YAML file and running the calculation of those functors on the deepCoadd_obj tables.

Yusra AlSayyad let me know if you are able to review this. I was also thinking it might be good for Lauren MacArthur and/or Hsin-Fang Chiang to take a look also, since I think this is the biggest step so far toward replacing a large amount of the functionality currently in pipe_analysis.

BTW, the new relevant notebook demo has been moved to notebooks/coadd_demo.ipynb, and the old demo notebook have been sequestered into notebooks/old.

I'm putting most of the comments in github but its easier to track a global wish list here:

• Already talked about this, but I wish there was a template to repeat a functor on multiple filters, so we don't have to specify them 6X in the yaml.
• We'll want to add functors outside the qa_explorer/functors module. What do you think of a registry?
• The flux/magnitude calculations need to be right and we need FluxErrs and to use fluxMag0 error. I usually just copy: https://github.com/smonkewitz/scisql/blob/master/src/photometry.h
• Need to adapt to the flux-->_instFlux change.