Support for external user and room management

With this MR, two new configuration flags system.externalUserManagement and system.externalRoomManagement have been introduced. The code has been refactored, so it is no longer dependent on locally stored user and room entities. When externalRoomManagement is enabled, the service no longer sends room events and instead listens to them, so it can act when rooms are duplicated or deleted.

Furthermore, settings for focus mode and surveys have been moved into their own entity.