make a few things work. it doesn't immediately crash anymore
make some more things work. change userprohfile to userprofile again
make most things work
more fixes. make most tests work with the new usermodel
make is_external handle empty email adresses
remove obsolete code
add the PermissionMixin to the UserProfile and introduce the Staff Group. this makes all tests pass.
add a handmade userprofile migration
remove is_admin property