* preferences page improvements:
  * new <label>s for stylesheet selections
  * more padding
  * use id attribute, so <label> functionality works everywhere
* first attempt on a schema for the data from cpantesters.org
* block AppEngine-Google
* prepared support for META.json from search.cpan.org and using the
  api interface of metacpan.org

  But it's currently not used --- it seems that search.cpan.org nowadays
  provides a META.yml even if the dist has only META.json.

  If a META file could not be fetched, then an empty meta object is
  cached.
* cookie is now really persistent
  (https://github.com/eserte/cpan-testers-matrix/issues/4)

  Problem was that in the normal case (not updating preferences) the
  previous cookie object was reused, but this object was lacking the
  expires value, so the previous value was lost.

  Additionally, increased the expiration period from 10 years to 75
  years.