CORE-4600 Minor refactor in createFolder svc call.

Replaced parsing the result into a splittable with a call to the new Folder's getPath method.
CORE-4600 Fix for DiskResourceServiceFacadeImpl#saveSubFolders.

The saveSubFolders method now attempts to lookup any Folders already added to the store and update them.
Added a Folder#setFolders method in order to cache updated subfolders from service calls.
CORE-4600 Removed file caching in DiskResourceServiceFacadeImpl.

DiskResourceServiceFacadeImpl#getFolderContents always fetches updated data from the service, then updates any subfolders on success.