Move Twig-specific code from core to patternengine-php-twig #158

LineageHelper has some special handling for Twig. We should move this to patternengine-php-twig as core should be templating engine agnostic.

I think this should be possible to do by adding a PatternLabListener.php to patternengine-php-twig and hooking into patternData.lineageHelperStart or patternData.lineageHelperEnd.

@sghoweri Would you like to have a go at this? :)