Improvements to P·C·D·M and Ore modelling

Improvements to P·C·D·M and Ore modelling

- `ore:Proxy` is now a subclass of `anno:ResourceSelection`, via the
  new `ladys:Proxy` class (a Resource Selection which explicitly
  selects everything).

- P·C·D·M object property domains and ranges have been expanded to just
  `ore:Aggregation` where appropriate, enabling their use with other
  kinds of Aggregations.

- Ore Proxy properties now imply membership in the Aggregation that the
  Proxy is in.

- The use of `rel:previous` and `rel:next` for Proxies as specified by
  P·C·D·M has been documented and appropriate restrictions applied.