ol-ext: control Legend
computes a legend based on ol/styl/Style
and draw it on the map.
You can add or remove rows in the legend.
The control use a style or a feature with a style or a style functions to handle styles based on feature properties.
A select event is fired when click on the rows in the legend control.
You can use the getStyleImage() function to retrieve an image of a single style or feature.