Add reCAPTCHA support to Review Board.

Review Request #1214 — Created Nov. 13, 2009 and submitted — Latest diff uploaded

Information

Review Board
master

Reviewers

Add reCAPTCHA support to Review Board.

This change introduces optional support for captchas during the registration
process. reCAPTCHA is used for this, as it's pretty wide-spread, maintained,
has both visual and audio versions, works with or without JavaScript, and
has a nice side-effect of helping to scan old books.

Users can register accounts on http://www.recaptcha.net and enable captcha
support in the admin UI with the public and private keys provided on the
site.

This also splits off all the authentication-related settings into a dedicated
Authentication settings page.

Docs have been updated to talk about the new page and the captchas.
Tested the following scenarios:

* Registration without a captcha
* Registration with a captcha and a wrong answer
* Registration with a captcha and a right answer