Add configurable join message delay

[addstar]

This is just a simple change to allow the join message delay to be configurable.

By default, everything will remain the same for existing users, it should add the default value of 3 into the config.yml. I'm currently running this on my own network and it's working great.

I understand the concerns and hesitations discussed in #8 but I think there are scenarios (like ours) where we would rather have a more timely join message than a possible false one from a ban. We use proxy based bans (not relying on server bans) and players are refused almost immediately, even 1s is more than enough time to validate the player is connected.

[holli2801]

I love this, thanks for adding it, lets hope it can be added quickly. Or is there another way to get this before?

[EarthCow]

@holli2801 If you haven't built this yet I just built it today for myself here: BungeeJoinMessages-1.12.0.zip