chore(element-factory): add default size for group

lib/features/modeling/ElementFactory.js

@@ -187,6 +187,10 @@ ElementFactory.prototype._getDefaultSize = function(semantic) {
     return { width: 100, height: 30 };
   }
 
+  if (is(semantic, 'bpmn:Group')) {
+    return { width: 150, height: 120 };
+  }
+
   return { width: 100, height: 80 };
 };