Don't require an email source for sponsor

Self-registration by sponsor now works without having to define an email
authentication source
Fetch VLAN for dot1x only in internal sources

Fetching VLAN for dot1x connections is now limited to internal
authentication sources
Improve dropdown of authentication creation menu

Splitted internal and external classes in dropdown menu of
authentication types
Change background icon when no auth source
Fix error msg when deleting an auth source in use
Internal auth source must be sortable

Since dot1x connections use all internal sources to determine which role
to use, the order of the internal sources is important.