#89 Subnav items added to plugins settings show on every plugin settings...

... page
The handler function here takes a third parameter "data".  The value for this parameter varies by controller but in the case of "plugin_settings" the actual plugin is passed.  This allows you to do a conditional to make sure you can provide the right settings for the right plugin.  Your registration should look like:

```javascript
pb.AdminSubnavService.registerFor('plugin_settings', function(navKey, localization, plugin) {
  var pills = [];
  if (plugin.uid === 'porfolio') {
    pills.push({...});
  }
  return pills;
});