[SpecMap] - Treat Epics and Features as mapped when associated to an activity

At the moment, work items are only treated as mapped when they are represented as cards on the story map.

If I've associated an epic or feature to an activity, then it should be treated as 'mapped' (so it should not appear in the list unmapped items; and the SpecMap section on the WI should also show that the epic/feature has been mapped on this map.

If you also do https://support.specflow.org/hc/en-us/community/posts/360012776537--SpecMap-Associate-an-Epic-to-the-map, then any epic or feature which is associated to the whole map should also be treated as mapped.

Cheers!