Allow usage of default twig.js template resolver

[mihkeleidast]

This will:

• allow overriding twig.js template loader method in order to provide compatibility with twig.js (and PHP Twig) default behavior
• fix Include twig file from node_modules #42

Changing the template loading method does, unfortunately, break the fractal-specific functionality that the adapter provides, but it's clearly documented and you have to opt out of the fractal loader, so i think it should be fine.