Fixes several bugs and problems

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

src/main/java/net/knarcraft/blacksmith/util/TabCompleteValuesHelper.java

@@ -62,7 +62,7 @@ public final class TabCompleteValuesHelper {
     private static List<String> getAllEnchantments() {
         List<String> enchantments = new ArrayList<>();
         for (Enchantment enchantment : Enchantment.values()) {
-            enchantments.add(enchantment.toString());
+            enchantments.add(enchantment.getKey().getKey());
         }
         return enchantments;
     }