Port the NoCaptcha implementation of ReCaptcha from gh-5315

Close gh-5315

# Executive summary

This is a fork of the work done in gh-5315 by @nonumber to implement the new NoCaptcha feature of reCAPTCHA. Since the new noCAPTCHA API is incompatible with the parameters of the old reCAPTCHA implementation we have no implemented it as a new plugin called "Captcha-NoCaptcha". The same tests as gh-5315 apply to this PR.
Shoundn't the theme be ```light``` instead of ```clean```? The new API only supports light and dark