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

OPENCV_ANDROID_SDK - OpenCV Android SDK location (or OpenCV build dir)
Can be passed via ndk-build parameter or environment variable.

put the detection-based tracker back (to objdetect module), so that the Android face detection sample builds fine. The patch by Konstantin Matskevich that adds C++11 threads support has been merged in too. Also, fixed compile error in the doc builder.

Conflicts:
	modules/core/include/opencv2/core/cuda.hpp
	modules/cudacodec/src/thread.cpp
	modules/cudacodec/src/thread.hpp
	modules/superres/perf/perf_superres.cpp
	modules/superres/src/btv_l1_cuda.cpp
	modules/superres/src/optical_flow.cpp
	modules/videostab/src/global_motion.cpp
	modules/videostab/src/inpainting.cpp
	samples/cpp/stitching_detailed.cpp
	samples/cpp/videostab.cpp
	samples/gpu/stereo_multi.cpp

changed line281 -> line220
Presentation:
because line 220 give the globle var mDetectorType,and in line 230 it will be compared with mDeteorType !!!  it will never be unequal ~
fix:
change mDetectorType(previous globle var) to a new local val tmpDetectorType

super.onPause() call moved to begining of onPause method according Google recomandations.

FpsMeter class removed from Image Manipulations and Face Detection examples as unused code.

(#2569) simplifying code to avoid Eclipse CDT editor confusion, removing warnings and typos in comments

All samples use application style in android manifest instead of system calls in onCreate event now.

- Adding Android SDK/ADT r21 compatibility;
- fixing stl headers path for new ndk;
- fixing native API level for Android projects

Face detection package name replaced on org.opencv.facedetect for consistency with Google Play package.

Memory leak in color-blob-detection sample fixed;
Default face size in face-detection is set to 20%;
Error handling improved;
Some possible mat leak fixed;
Manager verison and engine interface version incremented to fix incompatibilities;
Docs updated;

Some unification done to simplify camera switching.

(cherry picked from commit 067744d0)

(cherry picked from commit bd12f636)
Signed-off-by: Andrey Kamaev <andrey.kamaev@itseez.com>