Initializes the Widget ui.

def __initialize_ui(self):
        """
        Initializes the Widget ui.
        """

        self.__margin_area_LinesNumbers_widget = LinesNumbers_QWidget(self)

        self.__set_extra_selections()

        self.__set_language_description()

        # Signals / Slots.
        self.blockCountChanged.connect(self.__margin_area_LinesNumbers_widget.set_editor_viewport_margins)
        self.updateRequest.connect(self.__margin_area_LinesNumbers_widget.update_rectangle)
        self.cursorPositionChanged.connect(self.__set_extra_selections)