added dimension blacklist/whitelist to dungeon main settings

[SanAndreaP]

added dimension blacklist/whitelist to dungeon main settings (spawn criteria), also fixed some settings issues:

• prevent loading of other custom settings during spawn, even if the "main" file with its inherits has criteria filters
• getCustom() should return null if it can't find a fitting custom setting
• SpawnCriteria biome lists are now checked if they're empty instead of checking for a null instance, as these should not be null, ever