CORE-4304 Added check to FileViewerWindow manifest errors.

Added a JSON parse check to FileViewerWindow manifest error messages, before attempting to decode them, which will prevent uncaught exceptions for non-JSON errors.
Updates for data config properties changes.

Individual data-mgmt endpoints are no longer defined as config properties.
Updated FileEditorServiceFacadeImpl to build endpoint URLs from the base URL configs.
Updated FileEditorServiceFacadeImpl to use the SharedServiceFacade since data-mgmt endpoints are now CAS secured.
Updated DiscoveryEnvironmentProperties to return only the base file-io URLs.
Updated FileDownloadServlet and FileUploadServlet to build endpoint URLs from these base URLs, and to use the CasServiceDispatcher where appropriate.
Updated the discoveryenvironment-example.properties file with the new config settings.