Some of the work currently done by LoadReferenceTask - the actual lookup of which shards overlap an area of interest - will be done by preflight (outside Task code) in the Gen3 era.  That will ultimately let us greatly simplify it, but in the meantime we will need to make sure it provides APIs appropriate for both CmdLineTask usage and SuperTask usage.

Reference catalogs also have a lot in common with catalogs of simulated objects we might want to insert into real images - they'll have different columns, but we'd want to shard them and look them up the same way.  We should look for opportunities in this refactor to support that use case as well.