Most current migrations add a field to a table/collection. The code
is always the same. So create a function to do the job.

Two things:


-  I believe the logo used on the top left of the new site isn't
   the latest version from Thorsten, we should export the latest
   vector and update it.
-  The text "Get started with the latest mediagoblin release" in
   the middle should have the "mediagoblin" replaced by a larger
   version of the logo.

Configuration files that support \_local versions (e.g.
mediagoblin.ini -- mediagoblin\_local.ini) should contain a comment
at the top, mentioning that a "\_local" version can be used (and
how that works).