upnp: Fix issue causing names of UPNP services to be messed up
audio: Fix assert() in pulseaudio when skipping to next video track

Caused by commands out of sync with internal decoder state
Rework how continous video playback build the video play list

We no longer rely on canonicalUrl to match the model but rather we keep
track of the actual properties that builds the model.

Fixes #1819
upnp: Use URL to video file as canonical URL

Since we no longer need canonicalUrl in order to do continuous play we
are much better of keeping the object ID away from it.

One upside is that Showtime now recognizes the same move in terms of
'seen', playcount, etc even if viewed from different folders on a UPNP server.
Tested with Twonky and MiniDLNA

Fixes #1788 (I hope)