Update the website-commit build

Summary:
Now uses GAE SDK 1.8.0, has a different email failure message, is less
spammy with email (only sends the first failure and then return to
success), and supports repository browsing with Kiln.

Test Plan:
Ran the new setup.sh on the ka-jenkins server.
Ran the website-commit build from jenkins.khanacademy.org

Reviewers: csilvers

Reviewed By: csilvers

Differential Revision: http://phabricator.khanacademy.org/D2459