Substitutions (and maybe other data entries) aren't deleted if they are out of validity

They aren't deleted if the start or end date of their validity range changes and they are out of this range.

added part::backend label

added source::customer label

marked #14 (closed) as a duplicate of this issue

marked this issue as related to #14 (closed)

moved from AlekSIS-App-Chronos#96 (moved)

assigned to @hansegucker

created merge request !48 (merged) to address this issue

mentioned in merge request !48 (merged)

mentioned in commit 4ea7bf88

closed with merge request !48 (merged)

mentioned in commit d751ee8a

closed with commit 4ea7bf88