Move FeatureInitParams initialization to Mineground

Passing a ton of arguments to the FeatureManager constructor doesn't
scale very well, and since Mineground owns most of the instances anyway,
we may as well initialize it in there.
Begin wiring up the onPlayerChat command

We'll use the "asynchronous" version of the event, and route it through
the ChatManager before firing the onPlayerChat event in features.
Support the /login command, implement basic login flow

/login is the more obvious way for players to identify themselves. There
will be an automatic flow available for players who have recently played
on the server as well.
Automatically identify players who played recently

If a player played in the past 24 hours using the same IP address as
their current session, log them in automatically. Given the average age
of Minecraft players I'm looking forward to the "OMG BUT MY BROTHER DID
IT" excuses already.