Chocolate Candy Cheesecake

1 cup graham cracker crumbs
1 egg white, slightly beaten
1 tablespoon light butter or margarine
1 − 8 oz. bar light cream cheese, softened
1 − 8 oz. bar fat−free cream cheese, softened
1/2 cup sugar
3 egg whites
1/3 cup unsweetened cocoa powder
1/2 cup plain nonfat yogurt
1 teaspoon vanilla extract
2 light Milky Way bars, cut up
1/4 cup fat−free caramel ice cream topping