Papercuts for the new user management frontend

[MorrisJobke]

Followup to #8824

• check out if we can improve the IE11 experience to be more like a table - it works, but is wrapped:

• creating a new user and try to close the "new user" row via the "X" button on the right does not work - closing it is only possible by clicking the "+ Add new user" button in the sidebar

• Removing groups does not update subadmins list

[skjnldsv]

creating a new user and try to close the "new user" row via the "X" button on the right does not work - closing it is only possible by clicking the "+ Add new user" button in the sidebar

This button is here to reset the form, not close it :)
That's the behavior we had on the previous list ;)