Separate namespaces for domains involving VA (and others)

[gatemezing]

In some examples, there is a reference to the prefix erava: - we need to resolve to a stable URI.

[Certiman]

The namespace erava: was reserved for internal resources only relevant in the context of the vehicle authorisation process. At the moment, we do not need these externally, as era: and vpa: suffice.

There may be one exception in the future: ontology for VA-documents and -applications may be located under a separate namespace (instances will all be non-public, and this approach is not legally supported at the moment).

[Interoperable-data]

Current status on namespaces:

1. We must assume very long-term usage, and hence should no longer refer to Register names as they exist now. It is better to use "domains", like railway subsystem names or terms which will not be removed, like VehicleType.
2. In the current onto, and this is a known imperfection, many era:-properties & classes already have such a more precise context. With the vehicle register now modeled as well, we notice a more urgent need to add namespaces for "domains".
3. Also the data instances are to be given a location prefix, which cannot be era: either.

(mdh)