Options dialog: Use our own constant instead of hijacking a predefined constant.
Fix resetting the settings from the "Options" dialog.

There could be some race between the closing instance of MPC-HC and the newly opened one.

Also MPC-HC was restarted too aggressively leading the exiting program to crash during exit.

Fixes #4938.
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.