for non-ANDROID platforms

(2.4) Backports from master branch (#7854)

To resolve undefined "Mat_to_vector_KeyPoint" error

This reverts part of commit 0db10a30

refactored; added Camera2, notify callbacks, front/back maxCamera sizes; disable new stuff if target API < 21

`-E touch` command doesn't create intermediate directories. We have to do it
manually using `file(MAKE_DIRECTORY ...)` command.

- Substituted HAVE_WINRT with WINRT
- Fixed compilation issues in ocl.cpp and parallel.cpp
- Fixed compiler issue for WP8: "C2678: binary '+' : no operator found which takes a left-hand - Fixed gitignore
- Added #ifdef HAVE_OPENCL to remove compiler warnings in ocl.cpp
- Used NO_GETENV similar to '3rdparty\libjpeg\jmemmgr.c;
- Added ole32.lib for core module (for WindowsStore 8.0 builds)
- Made OpenCV_ARCH aware of ARM
Signed-off-by: Maxim Kostin <v-maxkos@microsoft.com>

- added java wrapper
- disabled python wrapper