Require user to enter nickname and host when logging in

mentioned in merge request !9 (merged)

closed via merge request !9 (merged)

closed via commit fea370c2

Why should the host be required? Neither pleroma-fe nor mastofe are using this format, I guess this would make sense to allow it to be specified to be useable as a standalone version but it makes none to require it when it's included with the backend.