Add missing null check in HUDStopModuleWatchingPacket
Go over all users of getLogisticsModule and add null checks.
Whoops, _fluidIdentifierCache can contain nulls. Fixes #395
Rewrite ItemIdentifier again.
Variants with no NBT are kept forever, variants with tags are WeakRef'd and cleaned up by a daemon thread.
Damage and maxstacksize now ask using a itemStack.
Cache masStackSize.
Remove some of the ItemIdentifier/ItemStack duplication for methods.
Merge branch 'mc16' into mc16_block