Add logic to routing for visual group based menus

Continuing on from #65 this adjusts the routing logic to ensure that menu items which use a visual group to filter on should generate a correct menu item.  This moves the `vgroupid` field to the request section of the menu item editor, adds the ID to the menu lookup as needed, and adjusts the `ArsModelBrowses` model to check for the ID in the request first and then fall back to the params.  For testing, I've pushed these changes to the `joomla.org` project as well as my own website to verify that routes with the new logic are correctly built and that existing routes are unaffected.