find_block using openCV

Create a new method [using openCV](https://stackoverflow.com/questions/15729210/how-to-draw-a-rectangle-around-an-object-using-some-opencv-algorithm/15730095) to detect rectangular windows from a 2d array of probabilities, replacing [find_block (line 75)](https://github.com/PatrickC05/WindowCleaningProject/blob/master/Detection/WindowRecognitionSimpleMethod.py) 

