Spirit Grindstone

The Spirit Grindstone is a Djinni infusion. This grindstone has some differences:

1. Remove only curses from enchanted items;
2. The returned XP is 100%% of removed curses (instead 50%%-100%%);
3. When combining two items, the enchantments of the top one will be maintained;
4. The repair rate gets an extra bonus, sum of durability values plus 20%% (instead of just 5%% of maximum durability), so repairing at the right time will be rewarding;