Most importantly, added support for multiple include directores,
but also did some general cleanup.

Python 3 requires METH_VARARGS | METH_KEYWORDS, not just METH_KEYWORDS.

In these cases, just using print() is enough to ensure py2/3
compatibility.

Added a header with defines to enable the module to compile with either
python 2 or 3 without changes.

This protects from unwanted implicit conversions between types at compile time.

Also move cv::linemod to own header

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

* Drop some low level API
* Remove outdated overloads
* Utilize Input/OutputArray

This makes arguments of type InputOutputArray required in python unless they
have a default value in C++.

As result following python functions changes signatures in non-trivial way:

* calcOpticalFlowFarneback
* calcOpticalFlowPyrLK
* calibrateCamera
* findContours
* findTransformECC
* floodFill
* kmeans
* PCACompute
* stereoCalibrate

And the following functions become return their modified inputs as a return
value:

* accumulate
* accumulateProduct
* accumulateSquare
* accumulateWeighted
* circle
* completeSymm
* cornerSubPix
* drawChessboardCorners
* drawContours
* drawDataMatrixCodes
* ellipse
* fillConvexPoly
* fillPoly
* filterSpeckles
* grabCut
* insertChannel
* line
* patchNaNs
* polylines
* randn
* randShuffle
* randu
* rectangle
* setIdentity
* updateMotionHistory
* validateDisparity
* watershed