[FEATURE] Custom Item Rarities

[MentalReject]

A way to add additional item rarities and possibly rarity colors to further enhance magical item appearance

[Larkinabout]

Seems easy enough to add new item rarities via the config, so I can add a menu for it. Not sure about the colours though as it doesn't look like there's a config for them and they're likely hardcoded in the CSS. Might need a system development, but I'll look into it.

[Larkinabout]

Added in 0.12.4.