Schema additions and ID code cleanup

Fix bug with duplicated tenantID when updateFeedPaths is called (it
took the already formatted ID from add or remove activity and passed it
to follow and unfollow entity, where the tenant ID was prepended again)
Centralize ID building for vertices (now only in
getOrCreateEntityVertex and serializeActivity)
Remove IDs from edges
Add formatted IDs to activities
Add Vertex Type properties
Add Created properties
Add EntityID to all nodes and edges related to an entity
Add ActivityID to activity nodes