* Renamed files for consistency reasons
err_school.go implements the full education interface not just schools.
ldap_school.go renamed to ldap_education_school.go for making it
consistent with ldap_education_user.go
* graph: Add stubs for education/classes endpoints
The acutal backend implementations are still empty.
* First iteration of a groups test
* Do not render a result in case of an error
* Generate mocks for identity.Backend
* Export listResponse (-> ListResponse)
* Add unit tests for GetGroups
* Finish GetGroups unit tests
* Increase test coverage
* Increase test coverage
* Increase test coverage
* Add missing mocks
* Fix return codes
* Fix error messages
