Twig and Plates renderers update

Updated classes of Twig and Plates renderers.

New class: TwigLoader - an extension of Twig_Loader_Filesystem with support of file extensions.

Twig renderer is stil an extension of core Twig Environment. But Plates renderer is now just a wrapper, because the framework is going to change dramaticaly.

The possible problem is that in new version the template object is being constructed with template name as an argument, while in previous version and in Twig the template name is being passed on render.