Django 2.2 removed some deprecated functionality, added new requirements

for multi-database unit tests, and again changed how table and index

names are normalized/hashed.
This change adds in compatibility for much of Django 2.2, minus some

work that still needs to be performed in SQLite (which many of the

recent changes works toward).
This does not implement the new Meta.constraints functionality, which

will need to be handled in another change.

Most unit tests pass on Django 2.2 (and earlier versions). As this is not

a complete compatibility change, there's still work that needs to be done

before we can claim 2.2 support.