Added keep-greater-slot option in SmithItemEvent listener config, if enabled, even new generated slot value smaller than existed slot value, we will still keep use existed value as new upgraded item's slot limit.
Fixed the issue where the client displayed wrong level when the anvil was unable to add enchantments to an item due to the enchanting slot being full.
Player level never been taken by EnchantmentSlots, it just a client-side display issue.