Alert the user for future postgresql-contrib dependency

Future versions of Stoq will requires postgresql-contrib package to be
installed on the server. Here we are doing some changes to facilitate the
transition:

* For new installations, install postgresql-contrib too
* For existing installations, alert for the need of the package and, if the
  database is installed locally, offer a link to install it using "apt:"
  protocol

Change-Id: I73ac7290572b632cccbe6d3840778a6481c3c99a
Update translations

Change-Id: I5138a003cdc1efc6722339f1b28bc218e30bc1b4