New Features for the container

[ETES-Stuttgart]

Hi Michael,

thank you very much for your excellent work.

We have added a few new features to your container, which we would like to share with you:

• Make invite status filter configurable
• skip empty groups
• allow to add custom user attributes
• add virtual groups for every role in every group
• set default username based on firstname.lastname

Every feature except the default username can be configured and is disabled by default so no behavior will change.
I created the features in separate branches within our repository, but I decided to create one merge request to make merging easier for you.
If you have any suggestions for improvement, please let me know.

Best regards,
Paul

[Pflum]

Another small fix, I moved the default values to the site, so the default applies also to sites defined in the "sites" part of the config.