Add permission based drops

[shantek]

Add the ability to lock a specific drop behind a permission that has been created in the drop config.

For example, of they create larger drops for Shulkers and want it as a vip drop, they should be able to assign "shulkervip" as the permission, so this would require the player to have shantek.custommobsrops.shulkervip to get these custom drops.

If a player then has permissions for multiple drop types for the same mob type, we should then just grab the first valid option from the config and use that.