Automatic legend

Would be great if the legend is printed automatically when `simdec.visualization` is called. 
Now it needs a few more lines:

```
from IPython.display import display, HTML

legend_df, styler = simdec.tableau(
    var_names=dec.var_names,
    statistic=dec.statistic,
    states=dec.states,
    bins=dec.bins,
    palette=simdec.palette(dec.states),
)

display(styler)
```