Add automated tests before production deployment

[MattBlissett]

We have some basic tests shown in vocabulary.md:

for i in core/**/*.xml core/**/*.xml extension/**/*.xml sandbox/extension/**/*.xml; do
    xmllint --noout --schema schema/extension.xsd $i
    echo
done

This should be run before deployments (sandbox and prod) and for prod include additional verifications for links (not to the sandbox, target already exists or is to be deployed).