Support embedded cover-art.

This will probably work only with our custom internal LAV Splitter currently. However the code should be able to load the cover from any splitter exhibiting the IDSMResourceBag interface.

Fixes #4941.
Fix: Be less aggressive when loading cover-art.

If no author name is available, don't load a random image.
LAV Filters: Distribute CHANGELOG.txt, README.txt, COPYING files (PoC).
Don't force any background color for the Shockwave graph.

This commit fixes #1747.
WebUI: Inform the web interface that no audio stream is available.
WebUI: Make use of new [hasaudio] info.