Add feature to revert all changes done by Background Muter

[nefares]

In some cases applications previously muted by the background muter stay muted even though it exited cleanly. This can happen when the respective application exits while being muted

A possible fix for this is to store all apps encountered by background muter on the hard drive and each time it exits make sure that all those apps were properly unmuted.

A less ressource heavy option may be to store the encountered apps in memory and unmute them (even if they are no longer running), or to detect when an application being muted exits.

The code will likely reside in RunMuter() to compare the previous list and current list when the timer ticks and so detect any changes