GUACAMOLE-526: Add convenience callback for displaying modal notifications strictly for REST errors, while logging all other promise rejections.

guacamole/src/main/webapp/app/rest/restModule.js

@@ -21,4 +21,7 @@
  * The module for code relating to communication with the REST API of the
  * Guacamole web application.
  */
-angular.module('rest', ['auth']);
+angular.module('rest', [
+    'auth',
+    'notification'
+]);