Modifier Deck Holder for Gloomhaven

UPDATE: Added V2 with material removed for less filament use, raised wall height to keep from seeing the color of the last card, and put a slope in bottom of the vertical car holder to keep them tipped back.

Inspired by [Gloomhaven Battle Deck Holder by nxumdon](https://www.thingiverse.com/thing:2757600). Made it harder for players to see the front of the bottom card.