Change phabricator to be ssl-only!

Summary:
Now requests to http will redirect to https.

This is how epriestley does this at phabricator.com, rather than using
the ssl_required config option inside phabricator, which is actually
harder to configure (you need to pass in the HTTPS environment
variable properly, from nginx).

Test Plan:
Fingers crossed.  I'll install this on the phabricator machine and see
what happens!

Reviewers: chris, alpert

Reviewed By: alpert

Differential Revision: https://phabricator.khanacademy.org/D14818