added video writer quality, which user may change dynamically in the case of motion jpeg; enabled NEON intrinsics in the encoder

In MacOSx x64 it was getting a memory leak even without initializing points:
http://code.opencv.org/issues/4250

Explicitly linking to a Python framework on OS X prevents modules from
being built against one Python (i.e. system python) and imported from
another (i.e. Homebrew python); the interpreter segfaults if there's a
linkage to a foreign Python. Building the module with `-undefined
dynamic_lookup` instead of an explicit link allows the symbols to be
resolved at load time from a compatible python.

HAVE_VFW flag is defined by CMake try_compile check.

Check fails for WINRT as vfw.h begins with

and contains empty set of functions for Store apps.

So we can safely remove vfw32.lib for WINRT in general

(independently of availability for specific configuration)

1. Use built-in mad() instead of += and *.
2. For stump stages, if weight.z == 0, avoid unnecessary calculation
because some features only have 2 rectangles..

It could improve
OCL_Cascade_Image_MinSize_CascadeClassifier.CascadeClassifier/*
about 10% mean values.
Signed-off-by: Yan Wang <yan.wang@linux.intel.com>