[xliff] Updated list of attribute values

Hi everyone,

Attached is an updated list of attribute values. I haven't added anything
from the XUL set, but a few other have been proposed. The XSLT style-sheet
to display the file has also been updated.

Christian: I've changed the way <appInfo> is used in the style-sheet, so we
can have examples, etc. at some point, as you suggested.

cheers,
-yves