Implement motion detection in slinky detection process

[filipbartek]

Restrict color detection to area of image that has changed in the previous frames. This should help suppress background noise.

OpenCV keywords:

• motion detection
• frame difference

(suggested by Borut)

[filipbartek]

Inspiring examples:

• Traffic counting based on OpenCV
• OpenCV motion tracking with python code

[filipbartek]

Some more cool key words:

• cv::calcOpticalFlowPyrLK
• background projection
• cv::meanShift