Add a function to add a "player" into the game.

[Ephreaym]

The idea is to add a "fake" player to the game so that it can be used as an owner for a bot. That way it'll show op on the scoreboard and show server population.

[dennwc]

We discussed a few options that we have here:

1. Use regular player object type (NewPlayer), but drop networking.
2. Research how the Player-NPC emulation functions work (engine has them already).
3. Check if we can use PhantomPlayer for it.