Added some protections and enhancements to Shop. Shop will not allow player to select more cards than is affordable. If Shop appears and player cannot afford a single card, both text displays will show '0' and clicking on the Start button will show a JOptionPane error message. Player will not be able to start a new round. (Should we bail the player out if this happens?) Ticket bank LABEL (not the actual ticket bank) now updates in real time when the up and down arrows are clicked: ticket bank label represents how many tickets will be left if the specified purchase is made. Shop constructor now has an optional int argument that can change the price of cards for that round.