API: test get concept matching keyword with factories.
API: test matching regex with factories.
API: test has relation with factories.
API: test supported languages with factories.
API: fix a test issue for getting available languages.
API: create method for fetching supergroups.
API: test supergroup fetching with factories.
API: adapt url requests in tests for the new urls file.
create a custom 500 handler view and templates for it.
API: raise exception for invalid method name.