Adds support for a new `ready` state in the template engine for arena signs.
A sign is in the `ready` state when there are players in the lobby and all of them have readied up. This is only relevant in arenas with start delay timers, as the arena session automatically starts when all players are ready otherwise.
The new state is completely optional, even when no base state is provided, and it inherits from the `joining` state when not defined.
Closes#593
Bobcat00
90d1f211fa