====== mute ======
**C → S → C: {type: 'mute', channel:..., muted...}**

mute – other end of call muted/unmuted its audio (mic) or video (cam)

If remote client mutes or unmutes its mic or cam a mute message is sent.

===== arguments =====
  * channel - string containing "audio" or "video" depending upon if mic or cam was muted or unmuted
  * muted - boolean, true meaning channel was muted (stop transmitting), false meaning channel was unmuted (started transmitting again)