More sorting options

[srnyx]

• RARITY_DESCENDING sorting type so that the rarest items are at the beginning.
• OWNED_RARITY_DESCENDING sorting type where items that are owned are at the beginning, then those items are sorted by rarity descending.
• Ability for players to select their own sorting type by changing something in the Settings menu.

Additional context Not really sure how these things haven't been added as they are usually must-haves for plugins like this.