Samsung images working using customised ProtoInfo

Added an extra contuctor to the Plainum.Manged ProtocolInfo class so
that we can create the object with the actaul protocol string in the
same manner than unmanaged developerrs can do. It's a part of the public
interface that missing in the Managed Version.
Used this new ability to provide thumnail resources for all video and
music (technically shouldn't be required for music but it doesn't hurt
to put them there). This change got us thumbnails on a Samsung Tv.
Made static api url handling first class citizen

Made static api url handling first class citizen, it was in there before
but it was rough test code, now it’s better structured and a bit
solider.
Reinstated some of the transcoding api url code.
Tried unsuccessfully to fix a date error reported by a dlna test
utility.