Fixes getting the name of enchantments
Fixes inconsistencies in material and enchantment name-checking
Allows using "null" or "-1" to unset per-material or per-enchantment configuration options
Fixes a bug where basePrice was set to a material name instead of the price for the material being displayed
Adds missing tab-completion for material/enchantment costs
Prevents inconsistencies in deciding if a value is null
