[OpenStack-I18n] Zanata upgrade to version 4

Hello, the translation phase for Queens is just over. Many thanks for all that work during the cycle and translations in different OpenStack projects. We will take the chance now to upgrade our translation platform to a new version. We don't expect bigger issues because we tested the upgrade process anyway on translate-dev.openstack.org. Nevertheless the platform could be not available this week. So please note the hint. kind regards Frank (PTL I18n)