Provide membership and hierarchy browser for Collections

[rob-metalinkage]

as per #64, collection membership and browsing is an important viewpoint. inverse of skos:member should be displayed.

ConceptSchemes should offer both hierarchy and collection views.

Note that SKOS Collections are the appropriate mechanism to group across multiple ConceptSchemes - so this facility will need to cater for identifying collections in other ConceptSchemes (but perhaps not expanding these by default)

[rob-metalinkage]

This facility has two parts:

1. the ability to group Vocabularies by Collection
2. the ability to show the collection heirarchy within a concept scheme

Collections (probably) only exist because they are important for the domain of use - so they need to be respected as a hint for preferred display.

An ability to mark a collection as "default" so it is displayed first and expanded by default would help - e.g. we may have collections of older versions we can hide, but have key things made visible. Perhaps a configurable condition triple to expand a collection - and show expanded ones first in the list of collections in the concept scheme?

[rob-metalinkage]

see opengeospatial/NamingAuthority#142 (comment) for further understanding of the potential requirement here.