Make JSON serialization consider IJavaScript tokens

[thrau]

currently

map.put("property", new JsCall("get", "foobar"));
new JsObject(map);

would translate into

{"property":{"function":{"identifier":"get"},"arguments":[{"value":"foo"}]}}

what would be more sensible is

{"property": get('foo')}

org.rauschig.wicketjs.util.JsonSerializer (more the jackson ObjectMapper) has to be adapted for this.