platinum: add support for xbmc specific fields dateadded, rating, votes and artwork

xbmc:dateadded to pass dateadded with items and not need to stat upnp resources for that
xbmc:rating for number-based rating
xbmc:votes for string-based votes number
xbmc:artwork for a type-url-based mapping of artwork
platinum: add SearchSync method to SyncMediaBrowser
platinum: implement GetSearchCapabilities in media browser
platinum: implement GetSortCapabilities in media browser
platinum: add patches for the new commits
upnp: set SearchCapabilities server state variable
upnp: add sorting support for upnp:episodeCount, upnp:episodeSeason, xbmc:rating, xbmc:dateadded and xbmc:votes
upnp: make use of dc:publisher by filling it with studios for videos
upnp: make use of xbmc:dateadded, xbmc:rating, xbmc:votes and xbmc:artwork