android: gradle-based package and samples

- drop hello-android sample

samples/android/tutorial-2-mixedprocessing/jni/CMakeLists.txt

@@ -0,0 +1,19 @@
+cmake_minimum_required(VERSION 3.6)
+
+# Enable C++11
+set(CMAKE_CXX_STANDARD 11)
+set(CMAKE_CXX_STANDARD_REQUIRED TRUE)
+
+set(target mixed_sample)
+project(${target} CXX)
+
+set(ANDROID_OPENCV_COMPONENTS "opencv_java" CACHE STRING "")
+message(STATUS "ANDROID_ABI=${ANDROID_ABI}")
+find_package(OpenCV REQUIRED COMPONENTS ${ANDROID_OPENCV_COMPONENTS})
+
+file(GLOB srcs *.cpp *.c)
+file(GLOB hdrs *.hpp *.h)
+
+include_directories("${CMAKE_CURRENT_LIST_DIR}")
+add_library(${target} SHARED ${srcs} ${hdrs})
+target_link_libraries(${target} ${ANDROID_OPENCV_COMPONENTS})