Develop the Gen3 Butler components as needed to support running all CmdLineTasks included in ci_hsc, via a testing script that calls their run methods directly (instead of using parseAndRun.

This will require (at least):

• A Butler class capable of supporting at least the get, put, and datasetExists operations. Expected to be developed by a combination of Pim Schellart [X] or Tim Jenness.
• A SQLite-based Registry implementation capable of supporting those operations. Expected to be developed primarily by Pim Schellart [X].
• A local POSIX Datastore implementation capable of supporting those operations. Expected to be developed primarily by Tim Jenness.
• A shim layer that allows these operations to be done with the Gen3 Butler using the Gen2 Butler API (particularly a temporary DataRef class). Expected to be developed primarily by Pim Schellart [X].
• A functional prototype definition of the Registry schema. Initial structure will be developed initially by Jim Bosch according to the general approach agreed at the January Middleware Meeting, with review support and additional content provided by others (especially Michelle Gower).
• A script to allow Gen2 Data Repositories to be loaded into Gen3 Registry databases and accessed by Gen3 Datastores. Expected to be developed primarily by Jim Bosch.
• A functional prototype for the Gen3 Butler's camera-customization interface (i.e. obs* package interface). Expected to be developed primarily by Jim Bosch, in consultation with Simon Krughoff and the obs redesign working group.
• A functional implementation of the Gen3 Butler's camera-customization interface for HSC. Expected to be developed primarily by Jim Bosch.
• Additional Registry/Datastore/shim functionality or minor CmdLineTask changes to support any use of methods beyond get, set, and datasetExists in CmdLineTasks (e.g. use of Butler.subset).

The completion of this epic is the first of two S18 Middleware milestones, with completion criteria the ability to run a custom version of the ci_hsc test package that uses the Gen3 Butler, with minimally modified versions of CmdLineTasks it executes. Our goal is to complete these tests by April 13.

This Epic should be used instead of the existing cycle-wide per-Team Epics by middleware developers members to organize the stories within its scope. Fritz Mueller will handle filling in the per-Team Epics as needed for loading PMCS.