Simplify and reduce RNG

The game was too complicated for new users, introducing new spells every turn in a match and completely overwhelming anyone who tries it out. In addition to that, the random nature of new spells every round was a bit too much in the RNG side, making the game feel less of a strategy game and more of a luck game.

To solve these, we've decided to remove the option to pick up spells during a match. This will reduce the possibilities of what you can do in a turn by a bit, which makes the starting deck much more significant.

To give the players more control of their starting decks, cards are now purchasable with coins that you get from beating stages in the Arena. Now you can more easily compose the deck that you prefer playing the most.