Replace templating by direct usage of twig engine

[GromNaN]

Symfony is slowly dropping the Templating component in favor to the direct usage of Twig Engine. Read this old comment by @fabpot and this blog post that highlight the performance impact.

Instead of injecting the @templating service into the renderers, what about injecting the @twig service?

Expected benefits:

• Better performances (smaller object stack to call)
• Easier overloading of templates thanks to namespaces

[yohannpoli]

We haven't performance problems at moment but if you want to make a PR for that, i agree with the idea.