Notable changes:
1. You can remove cards from your decks (so you can look at them!)
2. If you remove a card from the deck, it won't appear in your shulker when you join a dungeon
3. You can just put it back if you want to play with that card
4. Protection is in place to prevent players from putting competitive / practice cards in the wrong deck
5. You can't drop competitive cards, but you *can* drop practice cards (it will delete it from your deck)

Resolves #28