Add video call functionality

[chunweii]

Use Twilio video call API.

Also change Dockerfile to add utils as a dependency

To use:

• Add new variables to .env file

  TWILIO_ACCOUNT_SID=
  TWILIO_API_KEY=
  TWILIO_API_SECRET=

• Run the collab service and frontend
• Visit http://localhost:3000/room/1?userId=user2 or choose a different room/user id
• Visit http://localhost:3000/room/1?userId=user2&disableVideo=true if you don't want to use video (save cost)