Investigate state of a room when host disconnects

[kingdomlevel]

I'm not sure what will happen if the host:

• disconnects
• refreshes the page
• opens a new tab

... we probably need to figure out how to:

• pick up on a user disconnecting from a room (we can probably emit something from socket.io in server)
• recognising existing user when they open a new tab (json web token...?)
• assign a new host when the host disconnects entirely

... this one definitely needs some more thinking. Return to this whenever #13 is complete.

! depends on #13

[kingdomlevel]

The intended outcome of this behaviour should be something like:

• disconnecting client:
  • emit that they are disconnecting to inform other clients in the room
  • clear the localstorage item for this room's details
• the server will need to respond to the aforementioned emit by:
  • remove emitting client from allRooms global var in server-side app.js
  • IF HOST, assign a new host
  • emit to all other clients in the room that emitting client has left (+ who the new host is if emitting client was host)