title: Random order shuffle cv::Mat in OpenCV
body: <p>Is there no function in <code>OpenCV</code> to randomly shuffle a matrx (ordered by rows)?</p>
  
  <p>Input:</p>
  
  <pre><code>1 2 3
  4 5 6
  7 8 9
  </code></pre>
  
  <p>Output:</p>
  
  <pre><code>4 5 6
  7 8 9
  1 2 3
  </code></pre>
  
  <p>cv::randShuffle function only seems to randomly order the elements in the entire array
  I'm using the newer C++ API</p>