Better application of reactivity in the GameView page

[benjaminpjones]

This is just a demonstration of how the view can be improved, by relying more on Vue's reactivity system.

• Split up watchEffect, so certain effects run less often
• Don't perform any side-effects in setPlayingAs
• remove unsubscribeAllSeats - I felt this was a heavy-handed approach, since we really only need to unsub the currently subscribed seat
• Ensure we unsubscribe from the "unseated" topic (i.e. game/${id}
  • This last bullet is actually a change in functionality, and means we aren't always sending the seat: null "move" message

[benjaminpjones]

I had a bunch of pending comments, Oops. Hopefully they explain the changes in detail