Added a "sticky mode" option (disabled by default).

This mode will mean navigating from a managed tab to an unmanaged tab won't mute it until you navigate to another managed tab. The idea being you may like background noise but don't want 2 tabs playing at once.

Revert to manifest v2 to stop the callbacks being removed

Adds logging

When the background task worker was terminated, it forgot what tabs ought to be muted when it restarted. This fixes that.