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 is a potential security problem.  The service can be invoked with a relative path to access any file on the web server that the web server user has access to.  Well, not so much "access" as "pass to ogr2ogr", but it's hard to predict the security implications of that.  Probably better to just disallow specifying a local file path entirely.