New Feature: Export a Web map (LeafletJs)

[arky]

Export a Web map (LeafletJs) option will export observations as geojson file, referenced images and index.html file. This will enable Mapeo users to quickly publish their maps to their websites. This is feature that similar to current Mapeo web but provides more freedom for Mapeo users to customize and customize their maps.

We have received this request for a simpler way to share and embed observations on partners website. There is demo and source code

@gmaclennan I have asked @punwath to take shot at implementing a prototype file using sample mapeo data.