Select preferred/default merger site

I have a modified version of IFS called IFS Mobile. When I click a URL to IFS, I want to be redirected to an IFS Mobile version of the URL.

Avoid downloading the non-preferred site(s) if possible.

Every merger site should have a Prefer (or Make Default) button next to it on ZeroHello.

Start by tracing the ZeroHello merger-site list and the URL handling involved in selecting a site; the issue names no files or tests to begin with. Done means ZeroHello offers a Prefer or Make Default action for each merger site, redirects matching URLs to the preferred site, and avoids downloading non-preferred sites where possible.

索引モデルが issue の本文から書いたものです。