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.
Open dialog: Support quoted paths.

This makes the Open dialog behave consistently with Windows file dialogs.

Fixes #4954.
Open dialog: Cosmetics.

 - Give better names to functions and variables.
 - Reduce the visibility of member functions and variables.
STS.h: Give all parameters a name.

It's perfectly legal not to give a name to a parameter even if it is given a default value so this is only for cosmetic consistency.
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.