A small patch to allow the Twig view to work with Slim 2.3's view API

I think there is in an incompatibility between Slim 2.3's view API, and the current version of the Twig View shipped in Slim Extras.

I believe that the incompatibility was introduced when Slim started to use Slim sets (rather than PHP arrays) as the type of View#data: https://github.com/codeguy/Slim/commit/5ec3f4b169876c2a6807f8a88172e463cf56a35d

In brief, the render method of a Twig template expects an array, but a Slim set is now passed. I've fixed this by having the Twig view call the new all() method, rather than referring to $this->data directly.