R1:6b7183a76232

Modularize Aphront "sites"

Summary:
Fixes T5702. The path here is long and windy:

- I want to move `blog.phacility.com` to the new `secure` host.
- That host has `security.require-https` set, which I want to keep set (before, this was handled in a sort of hacky way at the nginx/preamble level, but I've cleaned up everything else now).
- Currently, that setting forces blogs to HTTPS too, which won't work.
- To let blogs be individually configurable, we need to either modularize site config or make…