Handle Network Disconnects

[MaxCWhitehead]

Description

Right now when a player disconnects, there isn't really any indication other than them stopping moving.

We should notify the player of this, and consider switching the remote player to an AI or something. That might be a bit more work - but some sort of toast message / discrete UI making known would be good.

[erlend-sh]

Ideally we would at the very least:

• pause game
• include a little notice that player dropped out.

[MaxCWhitehead]

This is partially handled - when all players DC, player is notified with option to leave game.

When only a subset of players DC'd, should continue game but add UI to indicate this.

This issue is relevant for disconnects outside of game / while still setting it up: #1004