Updated documentation to 2.2

- Added big note about changes in 2.2 for translation
- Updated references to Zend\I18n\Translator\Translator to either
  Zend\Validator\Translator\TranslatorInterface or Zend\Mvc\I18n\Translator.
Merge commit 'refs/pull/864/head' of github.com:zendframework/zf2-documentation into develop

PR #864