Prevent Witch of Greed from showing up in shops

[erasels]

A common design issue is common powers, none of these exist in base game. The issue this creates is that in shops, the guaranteed power card will be significantly weighted towards the common ones, making it harder to find the uncommon ones.

I would suggest using the SpawnModificationsCard interface from StSLib which has the method canSpawnShop. With this you could prevent the card from showing up in shops and preserve the general weighting that base game normally has with the rarity of the power cards offered in shops.