* Refactor Python Classes

(2.4) Backports from master branch (#7854)

Adding of destructor and placement new constructors for classes wrapped with CV_EXPORTS_W_SIMPLE macro

 - cv2.UMat implemented - python thin wrapper for UMat
 - no implicit copy from GPU to Host done, resulting UMat can be passed to next function without overhead
 - cv2.UMat.get() - to fetch data to Host
 - new tests covers: ORB, BFMatcher, goodFeaturesToTrack, calcOpticalFlowPyrLK

Add logic to avoid nonsense strides when dimension size is 1 and
NumPy is built with NPY_RELAXED_STRIDES from tripping OpenCV.

Conflicts:
	modules/gpu/perf/perf_imgproc.cpp

Cast a long integer to double explicitly.

Conflicts:
	modules/python/src2/cv2.cpp

Cast some matrix sizes to type int.

Change some vector mask types to unsigned.

Conflicts:
	modules/core/src/arithm.cpp

Previously the Python3 cv2 package ends up with no submodules (bgsegm, face,
etc) in it, which makes a lot of functionality unusable. By not writing over
our root reference we ensure the new submodules are added to the correct cv2
module.

The implicit narrowing in the initializer list throws a compiler error for some compilers with C++11 support turned on. The specific error message is: "error: narrowing conversion of 'PyInt_AsLong(((PyObject*)o))' from 'long int' to 'double' inside { }".

Tested on Clang 5.1.0 and Mac OS X 10.9.4.

maintain set of visited namespaces in CppHeaderParser
WARNING: REMOVED const name conversion (SomeConstName -> SOME_CONST_NAME), discussion needed

removed contrib, legacy and softcsscade modules; removed latentsvm and datamatrix detector from objdetect. removed haartraining and sft apps.
some of the stuff will be moved to opencv_contrib module.
in order to make this PR pass buildbot, please, comment off opencv_legacy, opencv_contrib and opencv_softcascade test runs.