Added an optional async update checker for dependent mods.
Prints e.g. "[Update] Collective has an update available: 8.0 -> 8.13" to the console.
Will ignore output completely if the server goes down.
The update checker can be disabled via the 'enableUpdateChecker' config option.

The complete changelog with previous versions can be found at:
  https://serilum.com/mods?changelog=collective