can't pickle cv2.GFTTDetector objects

[ihtishamaliktk]

I am getting these errors with every type of descriptor option available in the implementation. I have not worked before with multi-threading so I am not sure how to handle such an issue. The issue only shows up if visualization is TRUE. If I turn off visualization, the whole sequence is processed normally without any error.

P.S I am using Python on windows. All the builds were successful thanks to a user who wrote a guideline in the issue section about using this implementation on windows.

Thanks