Mjulian/login after merge upstream

Fixes a login problem after merging upstream master.

Fixes login after sogo uid change has been rolled back.

Added carddav logon operation bypass (login is already done against imap and caldav). Thus users with "username" and "not-username@domain.lan" configuration can login and use properly calendaring and mailing. Some deeper research will be needed here if we want to fix that limitation.

Please @bencer and @sixstone-qq review these changes.
It sounds quite reasonable to set it to null as we are bypassing this authentication. I wanted only to add code so future merges would avoid conflicts. Probably some logging would fit here so we should notice this behaviour. On my way. Than you.