Merge/review for cpratt/container_playlist_retrofit

Playlist support is now re-enabled for MediaContainers.

Changed the MediaContainer implementation to publish the (two) 
 supported playlist resources using MediaResources. This allows the
 playlist for of the URI, playlist handler, and a variety of special-
 case logic to be removed.

Moved the create_stream_source_for_resource() method from MediaItem
 to MediaObject so that MediaContainer can use it and it can be called 
 from the HTTMediaResourceHandler without a cast. Replaced "host_ip" as
 a param with HTTPRequest since the PlaylistDataSource requires access
 to the request's "hacks" parameter.

Moved serialize_resource_list() to MediaObject and made it usable
 by MediaFileItem, OdidMediaItem, and MediaContainer. 
 get_protocol_for_uri() went along for the ride.

Uncovered an issue with the MediaResource copy constructor. The
 ProtocolInfo wasn't being deep copied, resulting in some incorrect
 behavior with the MediaContainer. Added code to deep-copy the PI.

Playlists uncovered an issue with the assumed HTTP transfer mode.
 Per DLNA 7.5.4.3.2.33.2, the default transfer mode is "Streaming"
 *only* for AV content (not items, but content). For all other content
 forms, the default is supposed to be "Interactive". Added a 
 get_default_transfer_mode() to the HTTPGetHandler. The 
 HTTPMediaResourceHandler delegates to a newly-added MediaResource.
 default_transfer_mode() which returns "Streaming" if the streaming 
 bit is set and "Interactive" otherwise. The base HTTPGetHandler 
 returns "Interactive".