cmake: add BUILD_APPS_LIST

- build "opencv_version" only: `cmake -DBUILD_APPS_LIST=version ...`
- option 'BUILD_opencv_apps' should be 'ON'

apps/CMakeLists.txt

@@ -3,9 +3,22 @@ add_definitions(-D__OPENCV_APPS=1)
 
 link_libraries(${OPENCV_LINKER_LIBS})
 
-add_subdirectory(traincascade)
-add_subdirectory(createsamples)
-add_subdirectory(annotation)
-add_subdirectory(visualisation)
-add_subdirectory(interactive-calibration)
-add_subdirectory(version)
+macro(ocv_add_app directory)
+  if(DEFINED BUILD_APPS_LIST)
+    list(FIND BUILD_APPS_LIST ${directory} _index)
+    if (${_index} GREATER -1)
+      add_subdirectory(${directory})
+    else()
+      message(STATUS "Skip OpenCV app: ${directory}")
+    endif()
+  else()
+    add_subdirectory(${directory})
+  endif()
+endmacro()
+
+ocv_add_app(traincascade)
+ocv_add_app(createsamples)
+ocv_add_app(annotation)
+ocv_add_app(visualisation)
+ocv_add_app(interactive-calibration)
+ocv_add_app(version)