Goes to the next date based on the current mode and date.

def gotoNext( self ):
        """
        Goes to the next date based on the current mode and date.
        """
        scene = self.scene()
        date  = scene.currentDate()
        
        # go forward a day
        if ( scene.currentMode() == scene.Mode.Day ):
            scene.setCurrentDate(date.addDays(1))
        
        # go forward a week
        elif ( scene.currentMode() == scene.Mode.Week ):
            scene.setCurrentDate(date.addDays(7))
        
        # go forward a month
        elif ( scene.currentMode() == scene.Mode.Month ):
            scene.setCurrentDate(date.addMonths(1))