Clears out this toolbar from the system.

def clear(self):
        """
        Clears out this toolbar from the system.
        """
        # preserve the collapse button
        super(XToolBar, self).clear()
        
        # clears out the toolbar
        if self.isCollapsable():
            self._collapseButton = QToolButton(self)
            self._collapseButton.setAutoRaise(True)
            self._collapseButton.setSizePolicy(QSizePolicy.Expanding,
                                               QSizePolicy.Expanding)
            
            self.addWidget(self._collapseButton)
            self.refreshButton()
            
            # create connection
            self._collapseButton.clicked.connect(self.toggleCollapsed)
        
        elif self._collapseButton:
            self._collapseButton.setParent(None)
            self._collapseButton.deleteLater()
            self._collapseButton = None