force map model id to be integer

frontend-js/src/main/js/map/data/MapModel.js

@@ -357,7 +357,7 @@ MapModel.prototype.getId = function() {
 };
 
 MapModel.prototype.setId = function(id) {
-  this.id = id;
+  this.id = parseInt(id);
 };
 
 MapModel.prototype.getWidth = function() {