Creates a dependency for this item to the next item.  This item will
        be treated as the source, the other as the target.
        
        :param      item | <QGanttWidgetItem>

def addDependency(self, item):
        """
        Creates a dependency for this item to the next item.  This item will
        be treated as the source, the other as the target.
        
        :param      item | <QGanttWidgetItem>
        """
        if item in self._dependencies:
            return
        
        viewItem = XGanttDepItem(self, item)
        
        self._dependencies[item]        = viewItem
        item._reverseDependencies[self] = viewItem
        
        self.syncDependencies()