[#1309] Respect X-Forwarded-* headers
[#1309] Respect X-Forwarded-* headers

Specially `X-Forwarded-proto`, which controls the protocol used on redirects.
We need to redirect to the same protocol used by our proxy (HTTPS), regardless
if we are ourselves running HTTP or HTTPS.

openspending/openspending#1309

openspending/os-viewer,openspending/os-viewer,openspending/os-viewer,kravets-levko/os-viewer,kravets-levko/os-viewer,kravets-levko/os-viewer