Refactoring SLSim - Create Catalog class to ingest catalogs or simulation pipeline outputs.

[jacob-hjortlund]

Current Status

DeflectorBase and SourcePopBase currently ingest the outputs of SkyPyPipeline instance, the SCOTCH catalog, quasar.class.quasar_sample etc., which all require separate subclasses. Additionally these either a collection of galaxies or point sources, not covering the case where we want associations between the two, see #220. Part of the overall SLSim refactor, see #223.

Proposed Solution

Create a Catalog class that can be ingested by Population. The responsibility of the Catalog class is to adapt the output of a simulation pipeline, i.e SkyPyPipeline, or catalog to the format expected by SLSim and provide it for sampling by the Population class. It should be able to accept either a catalog of galaxies or point sources or both.

To-Do List

• Create base class.
• Create SkyPyCatalog subclass for SkyPyPipeline ingestion and adaptation.
• Create SCOTCHCatalog subclass for ingestion and adaptation of SCOTCH galaxy and transient catalogs.
• Add unit tests.