The singleton table SchemaVersion contains the current version
of the Hydra database schema. This can be used to upgrade the
schema on the fly.
Also reran the DBIx::Class schema loader.
releases as a dynamic view on the database was misguided, since
doing thing like adding a new job to a release set will invalidate
all old releases. So we rename release sets to views, and we'll
reintroduce releases as separate, static entities in the database.