Support verifiable claims

We need to start planning how the GC and our P/T partners will leverage the work currently being wrapped up by the W3C's [Verifiable Claims Working Group](https://www.w3.org/2017/vc/WG/).

Of particular interest is how we can leverage established data models (e.g. [NIEM](https://www.niem.gov/)) to express some of the claims that we are likely to need to enable both pan-Canadian and GC-internal trusted digital identity.

The issue names no files, tests, or entry points to inspect. Begin by reviewing the W3C Verifiable Claims Working Group and NIEM references, then define the claims and data-model integration needed for pan-Canadian and GC-internal trusted digital identity.

Written by the indexing model from the issue text.