Fix exception if api_client_authorization does not reference a valid user.
Ignore failure in data-migration part of old schema migration.

The migration should succeed if the Metadatum model did not exist in
the version of the project that was used to run the migration.
fix down-migration: add_column should have been remove_column
add a few fixtures and tests for API. refs #1517 refs #1510
Migrate the test database to 0 instead of trying to "drop database".

This way, the database credentials used for testing do not need
create/drop database privileges.
add note about running crunch jobs with no git repo at all