Evaluate if Split can be a Superclass method

[Edgar Carneiro]

Also this part on splits is extremely similar:

        // Divide keys, maximums and children by this node and its sibling
        let sibling: IBplusLeafNode = new IBplusLeafNode(
            this.order,
            this.parent,
            this.keys.splice(divIdx, sibSize),
            this.maximums.splice(divIdx, sibSize),
            this.children.splice(divIdx, sibSize)
        );
        sibling.setRightSibling(this.rightSibling);
        sibling.setLeftSibling(this);

        this.setRightSibling(sibling);
        this.parent.updateWithNewNode(this, sibling);