feat(flat-components): users panel

[hyrious]

Internal synced store / message change:

1. Added one storage whiteboard holding a map (Map<string, boolean>) of users with whiteboard access. Logic behind:

   fastboard.room.isWritable =
     isCreator ||
     onStageUsers[this.userUUID] ||
     whiteboard[this.userUUID]
   
   fastboard.room.disableDeviceInputs = !whiteboard[this.userUUID]

2. Added 3 peer commands about requesting/notifying device state, flow:

   // 1. teacher request some user to turn on camera
   teacher."request-device"({ roomUUID, camera: true }, userUUID)
   // 2. user turn on/off camera, send back one response
   user."request-device-response"({ roomUUID, camera: false }, ownerUUID)
   
   // `camera` above can also be `mic`

   When teacher turn off the device of some user, he will send one more peer command to this user:

   teacher."notify-device-off"({ roomUUID, camera: false }, userUUID)

@aderan @vince-hz