Merge branch 'feature_4172' into 'master'

Implemented https://project.math.uzh.ch/issues/4172



See merge request !10

javascript/src/QfqForm.js

@@ -688,6 +688,8 @@ var QfqNS = QfqNS || {};
         }
         var alert = new n.Alert(data.message, "error");
         alert.show();
+
+        this.setButtonEnabled(this.getDeleteButton(), false);
     };
 
     /**
@@ -1150,6 +1152,7 @@ var QfqNS = QfqNS || {};
         return !(!!this.form.$form.data('disable-return-key-submit'));
     };
 
+    // TODO: Ain't there a jQuery function accomplishing the same task
     n.QfqForm.prototype.appendQueryParametersToUrl = function (url, queryParameterObject) {
         var queryParameterString = $.param(queryParameterObject);
         if (url.indexOf('?') !== -1) {