Add local MultivaluedHashMap implementation

Add local MultivaluedHashMap implementation

The JSONRestconfService implementation contains a local UriInfo
implementation, SimpleUriInfo, that uses a MultivaluedHashMap
implementation from javax.ws.rs.core. This class is provided by
the dependency used at compile time however, the runtime bundle
that provides the javax.ws.rs.core interfaces doesn't provide
MultivaluedHashMap. Therefore I added our own local MultivaluedHashMap
class based on the external class. I also refactored SimpleUriInfo into
it's own class as it's used by both JSONRestconfService implementations.

Change-Id: I1af0771327d46c72e55facf14c41038fd583e0ed
Signed-off-by: Tom Pantelis <tompantelis@gmail.com>