Mbst 9478 sitemap improvements

1. Allow the base URI to be provided on the request, rather than just the hostname. This allows us to switch the proxying method while still supporting the old api
1. Use URI instead of curie, if there's no curie set
1. Output content and video URIs according to publisher-specific scheme
I think a consumer of the model should make their own decision about what they want from the hierarchy; it's dangerous to give helper methods like this, as they may not fully understand which parent to use, and blindly call a method like this.