enables Video I/O backend via Media NDK

* Add Android Media NDK video i/o file capture back-end

* Fix failing test

* Improve error handling/prevent resource leaks

* Add license text

* Modify default for WITH_ANDROID_MEDIANDK option

* Fix spelling of deleter_AMediaExtractor

* 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

https://github.com/gradle/gradle/tree/v4.6.0

License: Apache 2.0

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)

Avoids this error message with CMake 3.10:
CMake Error: CMake was unable to find a build program corresponding to "Ninja".
CMAKE_MAKE_PROGRAM is not set. You probably need to select a different build tool.

Related changes is that pkg-config tool is found (/usr/bin/pkg-config).

This makes it possible to compile OpenCV with for instance ndk-r16

OpenCV 3.4.0-rc

OpenCV 3.3.1

OpenCV 3.3.0

- eliminate CMake 3.5+ warnings
- removed usage of dropped "OPENCV_CAMERA_MODULES" variable
- partial support for Android NDK 11+

3.2.0-rc