wms proxy

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?

Revised a few more times by @dnahodil and @jkburges, looks mature now - has flag to enable/disable the feature.
It would be nice if we could have Portal.app.appConfig hold proper booleans. I assume there's a problem with that?