Fix admins not being saveable in UI.
Fix admins not being saveable in UI.

Due to how we save things now, we expect each model to at least have
some validations. So add a missing validation for the username, which is
probably a good idea anyway.

apinf/api-umbrella,apinf/api-umbrella,apinf/api-umbrella,NREL/api-umbrella,NREL/api-umbrella,NREL/api-umbrella,NREL/api-umbrella,apinf/api-umbrella,apinf/api-umbrella