Run the new update_github_teams.py script every 5 minutes.

Summary:
It will look for newly added github repos, and make sure that
they include the 'interns' and 'dev-fulltime' teams (adding them if
not).

Test Plan: Fingers crossed.

Reviewers: alpert

Differential Revision: http://phabricator.khanacademy.org/D13117
We use phabricator-files.ka.org as an alternative domain, for cookie security.

So we need nginx to forward it to phabricator-land the same it does
phabricator.ka.org!

Auditors: chris

Test plan:
Implemented this on toby and then visited
   http://phabricator.khanacademy.org/D13200
and saw the CSS load like it was supposed to.