Better shop.yml

[dkim19375]

Add a better shop.yml

• Add the ability to make items such as Magic Milk and stuff, maybe something like special-type: magic-milk
• Add item weights instead of hardcoding them, for ex if you have a weight: 5 item, you cannot purchase a weight: 1 item, with the default weight being 0, along with a weight-category
• Add items that can be downgraded on death - can be like downgrade: wood-pickaxe
• Configure the categories of the shop
• Add the ability to add cosmetic items in the GUI, for example glass panes on the bottom
• Configuration to run commands on purchase: commands: [ 'give %player_name% diamond_sword 1' ]