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

Yeah, making the convert service only work with URLs makes sense to me.  Might be worth verifying that `request.get` won't resolve `file://` URLs from the local file system, because that would open up the same problem.