Simplified views output from controller 

Added method which provides single point to render tpls that matching OpenCart convention from controllers with simplified code: `parent::outputTpl($data);`.

It was tested locally with catalog/controller/product/product.tpl file, see gist: https://gist.github.com/terales/cdcb5ecc27a49ded83d4

This is my first PR to OpenCart and any suggestion are welcome.