Fully qualified name <=> URL mapping

[smagi]

Clavis currently relies on some third-party component to resolve a continuation types from URLs. Future enhancements will require Clavis to perform this task as well, but:

1. Type URLs are ambiguous because the assembly name isn't part of the URL.
2. The UrlAttribute? allows continuations to declaratively customize their path.

The first could be resolved by a backwards incompatible change that includes the assembly in the path, ie. Foo.Bar, Baz <=> Baz-Foo/Bar, instead of just Foo/Bar as it currently is.

The second seems to necessitate a global assembly search for custom URL paths. Since we have to do this search anyway, it seems prudent to build the global mapping table at this point too instead of loading each mapping on demand.