Set lifetime for input forms

We may have to set lifetime for input forms because of recent activities on cross-site request forgery (CSRF). The form lifetime is successfully deployed in frameworks like web.py or plone etc. Proposed branch lp:~tkikuchi/mailman/form-lifetime implement lifetime in admin, admindb, options and edithtml interfaces. Other forms like create and rmlist have confirmation by password thus are safe regarding CSRF. The form generation time is set by a hidden parameter whose value is calculated following the mailman cookie algorithm. The default lifetime is set 1 hour in Default.py thus configurable by a site administrator. If a password is set in request, authorization cookie is discarded so the password authentication is forced. Wget tricks to manage list in FAQ can be used as they are now.