Revert "support admin_email config and pass through into blocking errors, return AuthError in all cases"

This reverts commit 0d43f991.

This is the first tranche of support for room versioning. It includes:
 * setting the default room version in the config file
 * new room_version param on the createRoom API
 * storing the version of newly-created rooms in the m.room.create event
 * fishing the version of existing rooms out of the m.room.create event