Core: fix delete topicmaps (#402).

Revealing a Topicmap topic inside the topicmap itself works. Deleting the Topicmap topic works.
(was broken with new storage layer.)

BREAKING CHANGES

AssociationModel: getOtherPlayerId() replaces getOtherRoleModel().

Just the player ID is returned (instad a RoleModel).
Circular associations are supported (start and end node are the same).

Close 402.