Make "Global Mute" available in the audio mixer

Although the master fader in the audio track mixer does not show a mute button it exists. When i work with Avid's Eucon controller software on a tablet the button shows up and i can mute all audio with one click.

This is a handy tool for example when switching between timeline and noisy sources in the source monitor, and since the function exists i would suggest to make it availabe as a button and - even better - a mappable key.