Make Core::Authority#staff_portal_uri configurable

What it says on the tin.

This PR also:

1. Contains fixes for NCS Navigator Authority's spec suite that I needed to run said suite.
2. Changes the interface for `NcsNavigator::Authorization::Core::Authority` by making that class' initializer accept an options hash rather than an `Aker::Configuration`.  I don't think this'll be extremely painful for clients.