Each value carries three things:

• id — the number. Needed for the few filters that bind as integers, notably
  classificationSubTypes.
• value — the camelCase name. This is what the equivalent field on a listing
  serialises to, so it is what to match on when reading a response.
• label — the display text, ready to render.

Values come from the enum itself at startup, so this always reflects what this build of
the API actually understands.

Sub-type ids are only unique within their classification family. A sub-type id of 1
means one thing under Offices and something else under Retail, so always read a sub-type
together with its classification type.