0.45.0: Default ttl per media type (#697)
* Adds support for default cache TTLs per Imp media types * Fixes bugs in tests * Fixes issues identified in PR review: * Refactors existing test into a JSON driven format, and adds new tests
* Adds support for default cache TTLs per Imp media types * Fixes bugs in tests * Fixes issues identified in PR review: * Refactors existing test into a JSON driven format, and adds new tests