Change all cards to extend CmCard.

Add a Category field to CmCard and let all cards extend CmCard to use
this field.

Change-Id: Ia5617ad196abda31aad3b0e609802d4385b808b7
Add a category field to CardData.

Change-Id: I872f5de5c7967cce0359f3a8287fd00d99ba5264