Add rarities to items

[cornerloan]

Items now have different rarities, which influence their chance to appear.
Relics may also need an outline with the color depending on the rarity of the item.

[LifeHckr]

Will have the place in code to do this from #148 but will still need to update sprites with outlines, and get relics based on rarities.

[LifeHckr]

#157 Closed