Drive auth config with the database

Summary: Ref T1536. This is the last major migration. Moves us over to the DB and drops all the config stuff.

Test Plan:
  - Ran the migration.
  - Saw all my old config brought forward and respected, with accurate settings.
  - Ran LDAP import.
  - Grepped for all removed config options.

Reviewers: btrahan, chad

Reviewed By: btrahan

CC: aran, wez

Maniphest Tasks: T1536

Differential Revision: https://secure.phabricator.com/D6243