Adds a new tag to the edit.
        
        :param      tag | <str>
        
        :return     <bool>

def addTag( self, tag ):
        """
        Adds a new tag to the edit.
        
        :param      tag | <str>
        
        :return     <bool>
        """
        if ( not (tag and self.isTagValid(tag)) ):
            return False
        
        self.blockSignals(True)
        create_item = self.createItem()
        if create_item:
            self.insertItem(self.row(create_item), XMultiTagItem(tag, self))
            create_item.setText('')
        else:
            self.addItem(XMultiTagItem(tag, self))
        self.blockSignals(False)
        
        if ( not self.signalsBlocked() ):
            self.tagCreated.emit(tag)
        
        return False