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/peopledetect.py

@@ -35,7 +35,9 @@ if __name__ == '__main__':
     hog = cv2.HOGDescriptor()
     hog.setSVMDetector( cv2.HOGDescriptor_getDefaultPeopleDetector() )
 
-    for fn in it.chain(*map(glob, sys.argv[1:])):
+
+    default = ['../data/basketball2.png '] if len(sys.argv[1:]) == 0 else []
+    for fn in it.chain(*map(glob, default + sys.argv[1:])):
         print(fn, ' - ',)
         try:
             img = cv2.imread(fn)