Deleting a topic or assoc does not remove it from other topicmap

Try this:

1. create a topic
2. create another topicmap and reveal the topic
3. switch back to first topicmap and delete the topic
4. switch to second topicmap. The now deleted topic is still visible there. If you select it a server-side error is thrown.

Happens in Beta-4 as well as Beta-5-SNAPSHOT.

Note: this issue is not related to client-sync. Only one Webclient instance runs. Client-sync is meanwhile fixed in Beta-5-SNAPSHOT, that is when two Webclient instances are running (e.g. in 2 tabs) the error does not occur. The deleted topic is properly removed.

This is a follow-up of #277

@irau FYI