Write a method called isMagicSquare that accepts a two-dimensional array of integers as a parameter and returns true if it is a magic square. A square matrix is a magic square if all of its row, column, and diagonal sums are equal. For example, [[2, 7, 6], [9, 5, 1], [4, 3, 8]] is a square matrix because all eight of the sums are exactly 15.