website translation infrastructure

[Graham Percival]

I believe that the translation infrastructure is now complete.  Edit
scripts/build/create-weblinks-itexi.py to change the translations for
links to manuals and whatnot.

See examples here:
http://lilypond.org/website/development.es.html

Note that I don't care if some of the current stable manual links are
broken, because some 2.13/2.14 manuals didn't exist in 2.12, so
there's not much we can do about that.  And the website isn't going to
become the main website until 2.14, so it's a non-issue.

Cheers,
- Graham