When a user moves a question category between contexts or an individual question between contexts they should be presented with a confirmation modal telling them that the action they are taking will result in some tag instances being deleted and get them to confirm that is ok.

At the moment we just silently delete those tag instances which isn't great.

The cases where a tag instance will be orphaned and deleted are when there are tags instance at a course level that loses access to the question:

1. system question with tags in c1 and c2 that gets moved into the c1 context (or an activity within c1) will result in tag instances in c2 being deleted
2. course category question with tags in c1 and c2 that gets moved into the c1 context (or an activity within c1) will result in tag instances in c2 being deleted