Add Exp costs/retrieval

Setting to enable retrieval of exp for repairs - like you get exp for mining coal. Also add this per item.

```
exp_get_from_repair: 100 #value between 0 and *exp for level 30*
```

Setting to enable exp costs to repair enchanted items - additional costs for repairing enchantments. Also add this per enchantment.

```
enchantment_exp_costs: 100 #value between 0 and *exp for level 30*
```
