Adds export option for layers

[jokd]

Fixes #1559

Should be used with caution and works only for vector layers. It exports the features that has been requested from the server, thus works best with geojson-layers or wfs with strategy:all but is primarily intended for draw layers.

Configured like this:

{
"name": "origo-cities",
"title": "Origokommuner",
"group": "root",
"source": "data/origo-cities-3857.geojson",
"style": "origo-logo",
"type": "GEOJSON",
"attributes": [
{
"name": "name"
}
],
"visible": true,
"exportable": true,
"exportFormat": "geojson" // ["geojson", "kml"]
}

exportFormat can be a string (geojson, gpx or kml) or an array of formats. Defaults to geojson in case om omitted or invalid.

[johnnyblasta]

It would be nice if exportFormat was case insensitive.

[jokd]

Right on Sloppy J

[johnnyblasta]

Right on Sloppy J

I was mainly thinking of the formats them self to be case insensitive, so you could write geojson or GEOJSON, kml or KML.

[jokd]

Have a go again. Now its very forgiving.
Could have done this transform in the export util instead but I put it in the same function as before.

[johnnyblasta]

Tested and works nicely.
When export to several formats is enabled a eleganter solution could have been implemented other than stacking on the menu, but I approve since probably one format is enhough in most cases.