Mute all tabs when listening

[jcambre]

We should mute all audio playing from the browser when the mic is open. At present, any time a user is playing audio through the speakers, it gets picked up as speech input and results in a failure. This may make for a somewhat confusing experience with the mute intent... a more ideal interaction might be to reduce the volume significantly (to say 20%) while listening, similar to how Alexa handles things.