Add isBalanced(), getHeight(), isSymmetric()

public boolean isBalanced()
Returns true if difference between heights of its left subtrees and right subtrees
is not more than 1 and left and right subtrees are balanced, otherwise return false

public int getHeight()
Returns the height of the BinaryTree on which this method is called
For a tree with just one node, the root node, the height is defined to be 0,
if there are 2 levels of nodes the height is 1 and so on
A null tree (no nodes except the null node) is defined to have a height of â1
Height of a tree is the depth of farthest most leaf node from the root (max depth)

public boolean isSymmetric()
Returns true if the left subtree of this node is the same as its right subtree in
values and shape