WIP: Resolve "Assignment active? method is not the same as filter result"

Closes #392 (closed)

reasons

• The index views active filter uses the scope active_or_not_yet_active
  • So the scope filters for assignments that are not returning true on assignment.active? beeing used within the assignment_status_badge helper

So this is rather a inconsistency between filter and view logic.

Description

https://trello.com/c/ZFfaGbLX/99-1h-filter-aktiv-inaktiv-funktioniert-nicht

https://staging.aoz-freiwillige.ch/assignments?q%5Bactive_or_not_yet_active%5D=true

The following inactive Assignement is shown: https://staging.aoz-freiwillige.ch/assignments/913/edit