[doc] rename several doc extension to *.rst to use the qt_snapshot sphinx directive

doc/widgets/mapping.md → doc/widgets/mapping.rst

 Mapping
 =======
 
-![image](icons/mywidget.png)
+.. snapshotqt:: orangecontrib/id06workflow/widgets/screenshots/mapping.py
+
 
 
 Signals

doc/widgets/shiftcorrection.md → doc/widgets/shiftcorrection.rst

 Shift Correction
 ================
 
-![image](icons/mywidget.png)
+.. snapshotqt:: orangecontrib/id06workflow/widgets/screenshots/shift.py
+
 
 
 Signals

orangecontrib/id06workflow/widgets/screenshots/com.py

 from silx.gui import qt
-from orangecontrib.id06workflow.widgets.com import ComOW
-from id06workflow.test import utils
-
-app = qt.QApplication([])
-widget = ComOW()
-# TODO: create a more realsitic dataset or store one on edna-site
-_map = utils.createRandomMap((200, 200))
-widget._process(_map)
-widget.show()
-app.exec_()
+
+def screenshot():
+    from orangecontrib.id06workflow.widgets.com import ComOW
+    from id06workflow.test import utils
+
+    app = qt.QApplication.instance() or qt.QApplication([])
+    widget = ComOW()
+    # TODO: create a more realsitic dataset or store one on edna-site
+    _map = utils.createRandomMap((200, 200))
+    widget._process(_map)
+    widget.show()
+    app.exec_()
+
+
+if __name__ == '__main__':
+    screenshot()