Allow an AJAX call to specify that it should not notify on error

Because there are some cases where it's OK to fail, and it's not the user's fault

cms/static/coffee/src/main.coffee

@@ -16,6 +16,8 @@ $ ->
     dataType: 'json'
 
   $(document).ajaxError (event, jqXHR, ajaxSettings, thrownError) ->
+    if ajaxSettings.notifyOnError is false
+      return
     msg = new CMS.Models.ErrorMessage(
         "title": gettext("Studio's having trouble saving your work")
         "message": jqXHR.responseText || gettext("This may be happening because of an error with our server or your internet connection. Try refreshing the page or making sure you are online.")