DDF-22 Updated transformer to do resource retrieval against fed sources

Updated the transformer to not only do resource retrieval locally but to
provide the source name of the metacard so if it is a federated source,
the federated source can resolve the resource request.
Added unit tests for modifications.
DDF-22 Added retrieve resource functionality to opensearch source

Added to the OpenSearch Source the ability to retrieve a resource using a
REST call to another DDF. Added unit tests and made changes to interfaces
to allow for mime type information to be returned.