Python samples adapted for Python3 compatibility

Common fixes:
- print function
- int / float division
- map, zip iterators in py3 but lists in py2

Known bugs with opencv 3.0.0
- digits.py, called via digits_video.py: https://github.com/Itseez/opencv/issues/4969
- gaussian_mix.py: https://github.com/Itseez/opencv/pull/4232
- video_v4l2.py: https://github.com/Itseez/opencv/pull/5474

Not working:
- letter_recog.py due to changed ml_StatModel.train() signature

samples/python2/video.py

@@ -182,7 +182,7 @@ if __name__ == '__main__':
     if len(sources) == 0:
         sources = [ 0 ]
 
-    caps = map(create_capture, sources)
+    caps = list(map(create_capture, sources))
     shot_idx = 0
     while True:
         imgs = []