CR: Mutex for interpreters

URL

https://dev.fairteaching.net/b/den-gwm-s1c-hlp

Current state

• Any interpreter (moderator) can choose a translation channel to speak to
• When there are multiple interpreters, both can speak at the same time

Desired state

• There should only be one interpreter allowed to speak at the same time
• Solution proposal:
  • There is a "mute" button for each chosen translation channel, see #12 (closed)
  • Interpreters are muted by default
  • When an interpreter clicks "unmute", it automatically mutes any other interpreter in the translation channel