Fixed a major bug: users weren't able to enter a 2nd CC card of a different type (nonAmex vs Amex).

Now they can enter various CC card types. Remvoed some CSS  in JS so that jquery's hide() function can used.
Also, the preventDefault is active only on the month field, but the month field will freeze up if two or more keys are
pressed at same time. This is the last major bug that still needs fixing.