use one mute-button for floor and interpretation mic

goal

• prevent user to have both mics (floor+interpretation) on at the same time
• provide intuitive feedback on which mic is selected
• buttons:
  • mute (original left button),
  • intrepretation channel (to speak into) --> floor is another option in the menu

detail: mute-logic

• the current solution uses some extra logic for inital mute-state of the interpreter-mic (#12 (closed), #32 (closed), #37 (closed))
• with this change, this is no longer neccessary
• initial mute-state can be taken from BBB-room-config (like normal)
• initial languange channel should always be "floor"
• when languages are switched, mute state (from user point of view) should not be changed: when mic is open before the switch, it should be open after the switch and vice versa

minimal version

• do not allow state "both mics are on at the same time"
• mute the other mic, when any mic is unmuted by the user
• (bbb logic for breakout-rooms has to be accounted for: resoring of mute state when returning from breakoutroom etc..)