Add a configuration to turn off the update checking.

This is so players are not blasted with chat messages every time they log into the game. This also allows modpack creators to use older releases without the pestering reminders about updates.

The update checker will be on by default. When turned off, then next time the server or game (if single player) is restarted the mod will not check for a version.

This has been addressed with version 1.1.1.1 which has just been released.