Ogr view model

Added an ogrItemViewModel that forwards files to our ogr2ogr service for conversion.
On drag and drop the file is uploaded to the server on a url it is loaded by the server.
Made this the default fall through for formats we don't have explicit handlers for.
Put 1MB size constraints on server and client side
Added airports.zip (shape file) to our init_test.json list

This string is shown to the user info in the info box, so it should be meaningful to users.  It can be kind of verbose, too.  Something like "Unknown / Converted to GeoJSON" maybe?