Add handling of deactived users on frontend

In the backend we can now deactivate users. We need to handle those on the frontend as well.

1. Display "Deactived contact" instead of given name and family name for users. Maybe also show this info greyish as well.
2. Stop the login for deactived users - so that they are not allowed to do something anymore. Show a page instead that they should contact an administrator to get back access to the sms.