Support permanent redirects between domains

[PeterJCLaw]

Currently our various incoming domains are all redirected as 302 to the canonical one:

• www.srobo.org
• srobo.org
• www.studentrobotics.org

It might be a good idea (for SEO) to make these permanent redirects (i.e: 308).

If we do add this we should ensure that we preserve fallback handling such that any tertiary domains handled incidentally by the same box (perhaps beta.studentrobotics.org if we bring that back) don't get clobbered.