A work-in-progress libre JS-based client for Google reCAPTCHA.

See: https://hydrillabugs.koszko.org/projects/haketilo/wiki/Roadmap#5-Development-of-a-user-controlled-captcha-client-107

TODO:
* Improve the demo script to re-run captcha in case our final token expires and
  to intelligently enable/disable form submission.
* Add support for dependencies of mappings on other mappings in
  Hydrilla&Haketilo.
* Craft an index.json.
* Make this client harder to distinguish from the original one:
  - Currently we're not sending some values that I have not yet figured out how
    to produce.
  - Currently we're possibly missing some delays that the original client does
    introduce.
* Add links to Google's Privacy Policy and ToS.
* Make automated tests.