Redirect to https

Summary:
If the phabricator.base-uri is set up with https and phabricator receives
a request that isn't over ssl, we will issue a redirect response to the user
to force them to use https.

Test Plan:
With this disabled, verified that pages still load correctly over http.
Enabled it; verified I get redirected to the same path but on https when I
make an http request; verified https requests get served without a redirect.

Reviewers: epriestley, vrana

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D3411