Added a new configuration setting for each bag - "failure-chance", which represents the chance of not receiving any item from the bag. Upon such failure, the user will experience a short random negative effect (blindness, poison, etc.). If "failure-chance" is set to 0, the bag will always spawn an item. The new setting does not affect drop chance from mobs.
Added 20% failure chance when opening the "Trick-or-Treat" box.
