Upload work to enable switching between rest and importer based upload workflow.

This PR is working toward making it easier to switch between the rest and importer based upload workflows. The rest side should work as before, but more work is needed on the importer side. There is also some duplicative code in geonode/static/geonode/js/upload/LayerInfo.js that still needs some work, but I'd prefer to get this in master now so I can continue my work there.