UPnP: Add the fraction of a second component to the 'Duration' attribute for music.

This is a no-op, it's entirely optional in the spec and we don't store
music duration to this resolution. I'm making the change because it
future proofs the upnp code should we ever decide to store music
duration down to the millisecond.

Refs #9632
UPnP: Ensure resource URIs are properly encoded and formatted.

Also fixed a couple of bugs.

1. The 'medium' size artwork was being defined
twice for video and recordings.
2. The thumbnail for recordings was using PNG which is within the
spec, but DLNA requires JPG be offered at a minimum. Since no client
will support PNG but not JPG, we may as well only offer JPG for now.

Refs #9632
Fixes #12202
UPnP: Ensure that all the values in the CDS Object XML are properly encoded.