enables Video I/O backend via Media NDK

* Add Android SDK debug build flag

* Change LOG_TAG define for consistency with other modules

* Android build improvements
* look for NDK in "ndk-bundle" directory under the SDK directory if location not specified
* look for cmake and ninja in "cmake" directory under the SDK directory if not found in the path
* disable use of ccache if not found in the path

* Redo build tool existence checks

OpenCV 3.4.5

- drop hello-android sample

OpenCV 3.4.4

tested with NDK 17b (17.1.4828580)

OpenCV 3.4.3

OpenCV 3.4.2

OpenCV 3.4.1

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

- configuration files for ABIs configuration
- use builtin Android NDK's toolchain by default (force flag to use OpenCV's toolchain)
- default values for 'work_dir' and 'opencv_dir'

- fix Javadoc:
  - generate Javadoc after gather step to process all Java files (including Android 21)
  - generate into 'OpenCV-android-sdk' directly without additional copy step
- use smart copy/move utility functions ('shutil' doesn't well with existed destination)
- by default move files to reduce pressure on storage I/O (> 800Mb)

OpenCV 3.4.0-rc

OpenCV 3.3.1

OpenCV 3.3.0

3.2.0-rc

- IPP is disabled by default when compiler is mingw (couldn't make it
work)
- fixed some warnings
- fixed some `__GNUC__` version checks (for correctness and convenience)
- removed UTF-8 BOM from hough.cpp (fixes #5253)