Filter by term while importing supervisions

Different as thought, Untis saves supervisions related to a term. As we don't filter supervisions by terms yet, this causes that the entries are overwritten by other entries.

added part::backend source::customer type::bug labels

created merge request !47 (merged) to address this issue

mentioned in merge request !47 (merged)

mentioned in commit 13482452

closed with merge request !47 (merged)

mentioned in commit e6e4aaab

closed with commit 13482452