Added BeforeHttpsRedirect hook allowing extensions to cancel forceHTTPS

For ZERO, we need to be able to avoid forceHTTPS from taking place in
case user logged in while on wifi, and later switched to
zero.wikipedia.org for the carrier who doesn't support HTTPS.
In that case, the extension will need to be able to cancel redirect
and force regular HTTP handling.

Open Question: should this code log off user in case hook returns false?

Bug 65567

Change-Id: If04c83066c5d47b3c04ad7674e3c4e95a4cd464b