Add Host property to IGameCreatedEvent

Add Host property to IGameCreatedEvent

When a game has just been created, it does not yet have any players in
them, and as a result you can't get the host or its connection id when
this event is called. This makes it annoying to link between this event
and the IGameCreationEvent that came just before it.

Having this link is useful for the usecase of a game code allocation
plugin that allocates codes from a pool, and needs to return codes to
a pool if these codes weren't picked.