Add a new update-translations job to sync translations with crowdin nightly.

Summary:
I created this on the jenkins console at
   http://jenkins.khanacademy.org/job
and then ran
   mkdir jenkins_home/jobs/update-translations
   touch jenkins_home/jobs/update-translations/config.xml
   ./fetch_jenkins_config.sh

It pulled in a few other minor changes that hadn't been checked in
yet, as well.

Test Plan: Fingers crossed!

Reviewers: chris

Reviewed By: chris

Differential Revision: http://phabricator.khanacademy.org/D2501