Map caption

[goord]

I am considering adding a 'map caption' section at the bottom of the story panel to display the variable, data source and attribution of the data shown on the map. There are other options but neither is perfect:

• Inline explaining what's shown may prevent a fluent story text and make it too academic,
• The attribution panel is rather hidden and is more suitable for the background maps (OSM, gebco, etc.) that have no significant role in the visualization.

The map caption support can be very lightweight CSS class for instance. More discussion with the dev-team may be fruitful here.

[goord]

Done with css in the stories-gijs branch