ReCaptcha feature
ReCaptcha config from setup script

Added config setting to be available from the ./setup script. Captcha
public and private keys are added in the Features->Security tab, the
captchaLogin is available in the New Server tab where you can enable or
disable reCaptcha for that server.
ReCaptcha https and CSP bug fixes
ReCaptcha error message
Recaptcha bug fixes

Error message for empty captcha "Please enter correct captcha!" and if
the user enters correct captcha but wrong login data it won't be
required to enter it next time.
Add name for utf8mb4
Merge branch 'RECAPTCHA2' of git://github.com/pbojan/phpmyadmin into pbojan-RECAPTCHA2

Conflicts:
	libraries/Header.class.php
Consistent config naming with other config options (issue #369)
Missing crossreferences in captcha doc (issue #369)
Add hint to captcha in security tips
Changelog entry
Merge branch 'master' of github.com:phpmyadmin/phpmyadmin