Minor changes in printing

D2TreeCore.java
 *Made some adjustments and further split the printing files into smaller (and hopefully more readable) chunks.

Misc
 *Added new message class (PrintRTMessage) that prints the routing table of a node.
Extend bug fixes, various changes in printing and small general improvement

D2TreeCore.java
* Improved check for first/second half of bucket extension in forwardExtendRequest(Message). Say goodbye to 3-children nodes and lost leaves.
* More informing messages.
* More verbose printing in printTree(Message).

ExtendRequest.java
* Not using the old optimal bucket size anymore.
* Made the initialNode variable private.
* Added a variable that shows whether we're extending the first half of the bucket or the second.
Extension bugfixes

D2Treecore.java
* During extension, adjacency links weren't properly created because some links were lost (the left adjacent node of old leaves was disconnected from it too soon). That happened because the old leaf has to act as an intermediary. It's fixed by modifying its direct adjacency links last.
* Minor changes to make the code more compact.