Implement captcha support

[fnagel]

Implement captcha support

[fnagel]

@criwe Some feedback regarding the real world capabilities of the current SPAM checks would be really useful!

[criwe]

Well, spam is really an annoying problem. Simple captchas don´t work at all. Honymoon traps do a good job on small formulars, but not in big ones. Using JS to submit the formular worked fine, but got one case it doesn´t worked anymore....
Some methodes used in wt_spamshield are a good thing: 1.) time used to fill the formular (it to short -> spam) 2.) count links in the text (if more than x -> spam).
A "bad-word-list" would may be an idea (saw that here: pw_comments)
A good formvalidation (i.e. emailadress) is a good thing too.

Only a good combination of anti-spam-methods will work in the longterm. Maybe it would be better to use something like wt_spamshild instead of implementing theses things on your own?

[fnagel]

Perhaps you can share some experience with the current implementation as well? My blog runs t3extblog for quite some time and in my experience the SPAM checks seem working pretty good.

Currently we have:

• Form validation
• Honeypot check
• Simple checkbox
• Cookie check
• Useragent check

There is a integration of EXT:sfpantispam (the old, t3blog related regex / blacklist extension) but this extension is not compatible with latest TYPO3 versions. We could replace this with a similar but maintained extension.

[criwe]

The current checks are working well atm. Spam was allways marked as spam. It think the methods are adequate for now. But we should keep other options in mind, if spamers getting more irritating.

[fnagel]

This seems currently the best captcha solution for 6.2 and 7.x: https://typo3.org/extensions/repository/view/jh_captcha/

[fnagel]

Related to #133