cleanup - delete JoinMessage.java
minor tweaks - removed default constructor in LookupResponse.java which was never used.
D2Tree.java

* Major success of rebel nodes. The authoritarian government is down. As a result, nodes are no longer obligated to live in the network and can now leave it at will. (Not really, it will be actually fully enabled as soon as some other kinks are tested/fixed)
* Nodes are filled with random value upon join. The value is constructed in such a way as to conform to the ascending (inorder) sorting.
* New function that generates a value (double) within an interval

D2TreeCore.java
* Added a copy constructor, used to move/copy/mirror a whole node to another.
* added a method that fixes broken links, used after a node has been replaced.

Misc
* (LeaveRequest.java) new class, used when nodes leave.