Refactor the last commit to fix broken tests.
Remove the duplicate forward slash from the gs/rest/layers url route. Fixes #1457.
Add geoserver context to the layer detail view and add the store_type helper.
Moves geoserver-specific url routes to the geoserver app.

* acls, resolve_user and layer_batch_download have been moved to /gs/acls, gs/resolve_user, and gs/download.
* The old routes (using the /layer prefix) still work, but should be removed once legacy code is updated.