BUG-997: Rework URLSchemaContextResolver

This patch introduces an alternative implementation of
URLSchemaContextResolver, which takes advantage of the newly-created
APIs. The core improvement lies in the fact that it pre-validates
registered sources, thus eliding multiple parse actions.

Change-Id: I3311a3f0251868f91c385d0291365934ccfb9ede
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "BUG-997: Rework URLSchemaContextResolver"