Implement Combo logic

 - Add the Combo tag in card data (hasCombo)
 - Store the cards played in  a Game.playedThisTurn list
 - Use combo() instead of action() if the card has a valid combo
 - Obey the REQ_TARGET_FOR_COMBO PlayRequirement
 - Implement SI:7 and add a test for it
Implement Minion.bounce(), with brewmaster tests