Add http->http redirection for Matrix/Riot

Doing this means that matrix-nginx-proxy now starts
occupying port 80, which necessitates that
SSL renewal happens slightly differently.

roles/matrix-server/templates/systemd/matrix-nginx-proxy.service.j2

@@ -12,6 +12,7 @@ Type=simple
 ExecStartPre=-/usr/bin/docker kill matrix-nginx-proxy
 ExecStartPre=-/usr/bin/docker rm matrix-nginx-proxy
 ExecStart=/usr/bin/docker run --rm --name matrix-nginx-proxy \
+			-p 80:80 \
 			-p 443:443 \
 			--link matrix-synapse:synapse \
 			--link matrix-riot-web:riot \