Workflow fixes and captcha support

We have made some changes:

* Captcha support for anonymous users (with recaptcha)
* Fixed workflows and add "Site Administrators" roles
* Fixed italian translations
* Enabled translations of anonymous author label in ploneboard views
* Update number of comments looking at the current users permissions
* Rejected comments can be modified from owners before submitting again
* Fixed return context in add_comment_script for users that can't access to the new comment (for example in a moderated workflow)

All features are made in separated commits.