[WIP] Initial blind lobby / game support

[past-due]

This PRs enables "blind" lobbies / games.

What is a "blind" lobby / game?

In a blind lobby: Players' true identities are hidden from everyone (except the host) - until the game starts
In a blind game: Players' true identities are hidden from everyone (except the host) - until the game ends

The host (currently, a spectator host) has the ability to see players' chosen player names / identities, and configure all of the game settings as expected (position, teams, etc).

You might want to also consider other configuration options, like blocking free chat, if you want to prevent players in the lobby from purposefully revealing their identities to each other.

What is the new "simple lobby" waiting room for blind lobbies / games?

A blind lobby / game can optionally be configured with an even simpler waiting room, which does not reveal the list of players, but simply:

• Basic information on the host
• The ability to check ready
• Basic status information on the lobby (number of ready players, whether waiting on the host to start the game, etc)

Implementation Details

When connecting to a game configured in any of the blind modes, each client will generate a unique new "blind identity" which is exchanged and used for communication with other clients. The host will receive the "true" player name / identity on join, which it can verify as appropriate, but will only share the "blind identity" and generic player names / details with all other clients.

Once the game begins (in "blind lobby" mode) or the game ends (in "blind game") mode, the host shares the host-verified "true" player names / identities with all other connected players. These are then "fixed-up" in the replay files so that replays play back with the true player names / identities revealed.