Positions of legend buttons #20
Description
The positions of legend buttons are not consistent -- for 3D scenes and quaternion spaces, the legend buttons are in the option panels; for time-series and UMAP graphs, the legend buttons are above the graphs. I think we can keep the current legend buttons, and add two legend buttons in the option panels, one for time-series graphs and the other one for UMAP graphs. By doing this, users can always find a button in the option panels to open the legend.