Remove unused PagePostAction2.
Remove terrible copyWithAnyMeOnPage and copyWithNewPageRoot.
Fix sidebar bug: don't break pages on which it's hidden.
Make embedded comments work again, remove terrible PageRequest stuff

- Let PageRequest be a class (not a case class)
- Remove terrible functions copyWithPreloadedPage and
  copyWithUpdatedPermissions
- Add http://server-address prefix in client/app/Server.ts so works
  also from embedded comments pages.
Merge branch 'topic-simplify-page-request'.