Adds a new view of the inputed view type.
        
        :param      viewType | <subclass of XView>
        
        :return     <XView> || None

def addView(self, viewType):
        """
        Adds a new view of the inputed view type.
        
        :param      viewType | <subclass of XView>
        
        :return     <XView> || None
        """
        if not viewType:
            return None
        
        view = viewType.createInstance(self, self.viewWidget())
        self.addTab(view, view.windowTitle())
        return view