wms proxy

DO NOT MERGE or MERGE AT YOUR OWN RISK!

Down the rabbit hole, a suggested fix for #946. I saw that authenticated geoserver requests go via the proxy controller, so why not just run them all through?

Have a crack at:
http://dfruehauf.emii.org.au

Still more work to be done here. I think that in general there should be a designated `openlayers` proxy in addition to the ProxyController.
It's a shame we need to strip the proxy URL stuff here. I haven't looked into the code yet but it would be good if we only added it right at the end just before we used the URL.