[automatic translation update] Updated 104 strings in 2 languages (ru, vi)

 Fixes ValueError: invalid literal for int() with base 10: '-' http://forum.piwik.org/read.php?2,106854
Reverting part of https://github.com/piwik/piwik/pull/120/files

automatic translation update
added new language: Vietnamese

Refs #4200, documented ScheduledTime a bit and added a factory method that can be used to create ScheduledTime instances w/ one line of code.

Refs #472 PrivacyManager support for Custom Events, so that when old data is purged, it works as expected for purging Segments as well.

Fix build, weird php bug PHP Fatal error:  Cannot use Piwik\Db as Db because the name is already in use in piwik-master/core/Tracker/TableLogAction.php on line 15