Implement contao templating engine.

The contao template engine allow us to use `$container->get('templating')->render('mod_x', ['foo' => 'bar']);` which renders the template `mod_x.html5`.
It's the same as do `$template = new FrontendTemplate('mod_x'); return $template->parse();` in the FE mode, or `$template = new BackendTemplate('mod_x'); return $template->parse();` in the BE mode.