[new B+ tree] Moved BTree related methods from BTreeUtils to BTree.
[new B+ tree] Moved remaining methods from BTreeUtils to the BTreeNode.
Merge remote-tracking branch 'origin/unique-non-unique-trees' into unique-non-unique-trees
[new B+ tree] Minor cleanup.
[new B+ tree] Refactored TestNode test.
[new B+ tree] Removed unneeded method.
[new B+ tree] Removed unneeded method. Code cleanup.