Added setting of new relic custom parameters

Added setting of new relic custom parameters

This enables better tracking of times measured by newrelic
@jcellary thanks, the only suggestion I would make is to move this [logic](https://github.com/Wikia/app/blob/MetricTransactionNames/extensions/wikia/Wall/WallBaseController.class.php#L123-129) to a separate function so that it doesn't clutter the controller (the controller method's focus should be marshaling data). I think it will improve the readability which helps with maintenance.