- properly detect Android SDK support of Ant/Gradle projects
- divide processing of And/Gradle based projects

CPATH entries are processed before any -isystem:
https://gcc.gnu.org/onlinedocs/cpp/Environment-Variables.html

- Recommended compiler checks:
  - GCC: CV_GCC
  - Clang: CV_CLANG
- fixed problem with CMAKE_CXX_COMPILER_ID=Clang/AppleClang mess on MacOSX
  Details: cmake --help-policy CMP0025
- do not declare Clang as GCC compiler

during opencv_world builds

add_dependencies(${target}) doesn't control regeneration of .apk file,
because "${target}" is dummy target.

When compiling with OpenNI2 flag active, CMake will not be able to find OpenNI.h due to the environment path not set in OpenCVFindOpenNI2.cmake. This PR rectifies this issue.

This suppresses the interpretation of string literals by switching the ocv_download_log from a macro to a function.
This avoid crashes when the string to log contains escape characters.

More details about the problem this PR fixes are available at: https://github.com/opencv/opencv_contrib/issues/1131

to reduce overhead of gradle builds

Added group targets for samples (opencv_samples, opencv_samples_<group>), install samples/data inseparate component 'samples_data'

- allow installing samples sources on all platforms
  even if BUILD_EXAMPLES is disabled,  fixed minor
  issues in sources installation process
- use 'example_<group>_<name>' scheme for target and binary file naming
- use single function for sample executable creation

Resolves CMake error after relaunch with updated source code:
Cannot find source file:
    modules/dnn/layers/layers_common.avx512_skx.cpp

* cmake: add ocv_get_smart_file_name() macro

* cmake: avoid adding files for unavailable dispatch modes

Read flags from 'cache' instead of resetting them

Found via `codespell -i 3 -w --skip="./3rdparty" -I ../opencv-whitelist.txt`

* Intel Inference Engine deep learning backend.

* OpenFace network using Inference Engine backend

* Do not build protobuf if dnn is disabled

* Added BUILD_LIST cmake option to the cache

* Moved protobuf to the top level

* Fixed static build

* Fixed world build

* fixup! Fixed world build

fix missing "opencv2/core/opencl" headers from core module (updated install list)