fixes for latest changes in opencv3.0 api

waitKey() normalization

fixed mser bindings

Also, removed the one from modules/python/src2/cv.py and cleared its
executable bit, since it's not a script.

    Update find_obj.py:
    Added additional error checking for the loaded files and modified the detector check to be more pythonic (is versus ==).

    Update common.py:
    Fixed a typo (contais -> contains)

added some sample description

rewritten feature_homography.py using it
added plane_ar.py - simple augmented reality sample

- switch btw threaded and non-threaded mode
- performance counters
- description

linetype -> lineType

Added gabor_threads.py sample

fixed "import cv" in the new python samples. corrected Python bindings to match the documentation and vice versa (NOTE: in cv2.stereoCalibrate the parameter ordering has been changed)

added square_size cmd line param for calibrate.py
added _coverage.py script to compute cv2 api coverage by samples (just for interest, may be removed later)

added color_histogram.py sample
work on VideoSynth (chessboard)