Case activities are forked

When users update activities on cases, a new activity is created rather than a separate revision. This means that if another user is viewing the activity and saves their own revision, you end up with two activities which should just be revisions of the first activity.

Activity IDs should not change every time you make a revision, rather a separate revision ID could be incremented. This would also simplify integration between systems because the ID for an activity wouldn't change every time someone edits it.