removed ERFilter (to be moved to opencv_contrib/modules/text) and lineMOD (to be moved to opencv_contrib/modules/rgbd)

- when IMREAD_UNCHANGED is set in flags, the tiff is read with 4 channels
- adding test for read/write

gen2.py reports headers it processes
cmake file restructured

The sanity check prevents Python 2 from calling findContours, because the
Python 2 bindings pass an empty matrix for `_contours`. If `_contours` is not
empty, the channel and depth check should determine whether the matrix is of
the correct type and size.

Note: the Python 2 bindings passes a matrix of type `STD_VECTOR_MAT` to
parameters of the type `OutputArrayOfArrays`.