[AppStream] A component kind for language packs

[Richard Hughes]

In Fedora we're adding support for system-wide language packs and I
really need to represent them in the AppStream metadata to avoid
hitting PK for lots of queries for each request in the software
center. The idea of a language packs is that's a virtual entity that
magically installs the right sub-package in various distro-provided
applications and keeps them up to date. So, kinda useful.

I'm thinking of using something like this as a prototype:

  <component type="langpack">
    <id>org.fedoraproject.LangPack-af</id>
    <name>Afrikaans</name>
  </component>

But I'm not terribly happy with 'langpack' as a type. Should we be
adding something like "lang" or "language" to the spec? I can't use
generic as I need to handle these in a special way in the software
center.

Richard