Add topic participants' info, amount of comment

* Added "Anonymous" as reserved username
* getCreatorName() now returns false (instead of message) if username is not available
* Display "Anonymous" as username instead of IPs
* Added post method and registerParticipants()
* Added post method and registerDescendantCount()
* Added message to display topic participants' info
* Added message to display amount of topic comments
* Added registerDescendant()
* Removed findDescendant(); use getRecursiveResult() after registerDescendant()
* Added registerRecursive(), getRecursiveResult() & descendRecursive()

These latter functions will make sure that descendant trees are not iterated
over too much. Multiple callbacks can be registered to descend the tree
recursively. Once the result for either of these is requests, all of them will
be executed in one go.

Change-Id: I3d1aedeebd595d24abbdb362e103860821d37a6f