code: def create_chan_labels(self):
          
          self.idx_label = []
          for one_grp in self.parent.channels.groups:
              for one_label in one_grp['chan_to_plot']:
                  item = QGraphicsSimpleTextItem(one_label)
                  item.setBrush(QBrush(QColor(one_grp['color'])))
                  item.setFlag(QGraphicsItem.ItemIgnoresTransformations)
                  self.idx_label.append(item)
docs: Create the channel labels, but don't plot them yet.
  
          Notes
          -----
          It's necessary to have the width of the labels, so that we can adjust
          the main scene.