adds import/export capability

We want to export the menu from our test instance and import it into production - this solves that issue as long as the [wwwroot] token is used.  If you like this functionality, it would probably be better to use a [siteurl] token as well/instead as [wwwroot] doesn't work well for sites in a subdirectory - eg. a site url of localhost/elgg exports as [wwwroot]/elgg

Either way, this is a good utility.