CMakeLists.txt for Android native activity added.

samples/android/native-activity/CMakeLists.txt

+set(sample example-native-activity)
+
+if(BUILD_FAT_JAVA_LIB)
+  set(native_deps opencv_java)
+else()
+  set(native_deps opencv_highgui opencv_imgproc)
+endif()
+
+add_android_project(${sample} "${CMAKE_CURRENT_SOURCE_DIR}" LIBRARY_DEPS ${OpenCV_BINARY_DIR} SDK_TARGET 9 ${ANDROID_SDK_TARGET} NATIVE_DEPS ${native_deps})
+if(TARGET ${sample})
+  add_dependencies(opencv_android_examples ${sample})
+endif()