added saving improvements

[owencompher]

10

• every drawing change (view.on("immediate-click") updates the object in local storage
• checks for existing object in local storage on map load
• changed load button to import button which prompts for .json file and loads it
• changed save button to export button which automatically downloads the map as json

loading the map object into local storage on every change might cause performance issues if there are many drawings, but I doubt it would very be noticeable unless there was an unreasonable amount of them

[MoffKalast]

Overall I really like the approach, it gives us the full functionality of having multiple maps, but outsources it to the local file system and file manager via exporting which was needed anyway. 👍