Merge pull request #13188 from alalek:samples_rename

* samples: rename starter_imagelist.cpp

* samples: rename intelperc_capture.cpp => videocapture_intelperc.cpp

* samples: rename openni_capture.cpp => videocapture_openni.cpp

* samples: rename image_sequence.cpp => videocapture_image_sequence.cpp

* samples: rename gstreamer_pipeline.cpp => videocapture_gstreamer_pipeline.cpp

* samples: rename autofocus.cpp => videocapture_gphoto2_autofocus.cpp

* samples: rename live_detect_qrcode.cpp => qrcode.cpp

doc/tutorials/videoio/intelperc.markdown

@@ -78,5 +78,5 @@ there are two flags that should be used to set/get property of the needed genera
     flag value is assumed by default if neither of the two possible values of the property is set.
 
 For more information please refer to the example of usage
-[intelperc_capture.cpp](https://github.com/opencv/opencv/tree/3.4/samples/cpp/intelperc_capture.cpp)
+[videocapture_intelperc.cpp](https://github.com/opencv/opencv/tree/3.4/samples/cpp/videocapture_intelperc.cpp)
 in opencv/samples/cpp folder.

doc/tutorials/videoio/kinect_openni.markdown

@@ -134,5 +134,5 @@ property. The following properties of cameras available through OpenNI interface
     -   CAP_OPENNI_DEPTH_GENERATOR_REGISTRATION = CAP_OPENNI_DEPTH_GENERATOR + CAP_PROP_OPENNI_REGISTRATION
 
 For more information please refer to the example of usage
-[openni_capture.cpp](https://github.com/opencv/opencv/tree/3.4/samples/cpp/openni_capture.cpp) in
+[videocapture_openni.cpp](https://github.com/opencv/opencv/tree/3.4/samples/cpp/videocapture_openni.cpp) in
 opencv/samples/cpp folder.