Added a way to generate the coordinates for symbols to place on the cards
Changed back.gif to card_back.gif
Massive cleanup of the CardImage module. Split the class into functions, so it no longer acts as a button. This allows a card to be constructed in a much more versatile way (no more weird hacks for blank cards or card backs). As well, the coordinates for the symbols are no longer hard-coded in, they are now generated on the fly based on the card and symbol sizes