Fix email notifications for @-replies that come via OStatus.

Fix email notifications for @-replies that come via OStatus.

* Moved notification sending from Notice::saveReplies to distrib queue handler, so it'll pull from the reply set we've saved regardless of how we got it.
* Set up gettext infrastructure for command-line scripts; gets localization mail notifications etc working from background queues.
* Adjusted locale switching: common_switch_locale() works at runtime for bg scripts, forces a message catalog update