samples: add videocapture_camera sample
samples: add videocapture_camera sample

- show capturing information: width / height / fps
- show average FPS for cap.read()+imshow() via cv::getTickCount()
- optional frame processing code path

opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv