Reworked API types used to attached additional information to tags, regions and licences

If we use a binary representation for the dataset of the and accept that the human-readable representations (TOML, JSON) do not round-trip, e.g. UMTHES are serialized as Umthes { id: 1234, label: "WRRL" } but deserialized as Umthes = 1234, we can simplify the types and infrastructure used to attach additional information in the API responses representing tags, regions and licenses. This absence of round-tripping should be palatable as the only writing human-readable datasets are we ourselves for manual datasets or in external harvesters.

Basically this means that LabelledTag, LabelledRegion and LinkedLicense fully replace Tag, Region and License in our RESTful API and are the only types which have to fully documented.