Implement WD4 restriction/penalty

[dgw]

This is the best, meanest, most sneaky card to have. Not only does the player get to call the next color played, but the next player has to pick 4 cards and forfeit his turn. There is a hitch, however (of course): you can only play this card when you don't have a card in your hand that matches the color of the card previously played.
Note: A player may have a matching number or word card of a different color in his hand and plays his "Wild Draw Four" card.
[…]
If a player plays a Wild Draw 4 card illegally and gets caught, he must first show his hand to the player who challenged. If guilty, he must draw 4 cards. If not guilty, the challenger must draw 2 cards in addition to the 4. The challenge can only be made by the person required to draw the four cards.
— http://www.wonkavator.com/uno/unorules.html