Refactored Twig scanner

[oscarotero]

@drzraf I've refactored your code to be more aligned with the gettext code.

• The TwigFunctionsScanner responsability is just extract the functions in the code.
• TwigScanner is a generical scanner for twig templates
• TimberScanner extends TwigScanner and has the handlers for the specific timber functions. I think this code should be moved to a different repository php-gettext/timber-scanner, but we can keep it here for now, for convenience.

The tests are failing. I'm not very familiarized with Timber or Twig, so just provided a basic structured code as basis.

[drzraf]

That's indeed way cleaner now. Added a couple of fixes. Testsuite green again.

[drzraf]

sorry to ask, but btw could you please grant me back the admin role on the repository.

[oscarotero]

Yes, sorry. You're admin now.