WW 4185 default json date format

This commit will allow configuration of the date format used by the JSON plugin.

The default can be set for all actions by adding the following to struts.xml

```
<constant name="struts.json.dateformat" value="yyyy-MM-dd"/>
```

It can also get set for each action eg:

```
@Result(type = "json", params = {"defaultDateFormat", "MM-yyyy-dd"})
public class ProjectsAction extends ActionSupport {
   //....
}
```