Slight changes to the extend mechanism

D2TreeCore.java
* After an extension, a bucket of 1 with nodes (2, 3, 4 ,5 ,6, 7, 8, 9, 10, 11, 12, 13) in it, splits into 2=(7, 3, 4, 5, 6), instead of 2=(3, 4, 5, 6, 7). The second bucket remains the same; 7=(8, 9, 10, 11, 12, 13). That lifts some load off of indexing, as only 3 node data need to be moved, while at the same time disrupting structural links as little as possible.
Indexing structure breakthrough. Keys apparently get to their correct place after an extension. Preparations for key movement after node redistribution.

KeyReplacementRequest.java
* New message-type class to facilitate the movement of values. You declare the destination node and the one initiating the migration and it does everything by itself. Only supports direct movement, inorder traversal to be implemented next.

D2Tree.java
* A key can be any double between -100K and 100K
* Streamlined printing process
* Extend decides what kind of key movement to run, if it's necessary.

D2TreeIndexCore.java
* The new method is the implementation of the key movement

D2TreeMessageT.java
* New messages added here as well.