initial work

Adding support for https://github.com/nelmio/NelmioApiDocBundle/issues/481

Missing:
- [ ] Review
- [x] Fallback to cookie storage
I would use ``\n`` rather tha n PHP_EOL (All newlines in template sources are converted to ``\n`` in Twig anyway, so it will not output PHP_EOL.

and having a second JS file alongside ``all.js`` feels weird