Enable nginx by default, and override the favicon to find the right tab easier

Enable nginx by default since we use it in production and it has broken things before ( https://gitlab.com/gitlab-org/gitlab-ce/issues/27054#note_21914305 )

Was also necessary (easier) to have a GDK-specific favicon for #186

Closes #186

Question: if we should use nginx infront of rails, should rails talk purely over unix-socket? Nginx currently binds on :3443 :3080 (TLS was removed)