Changed the way ships are drawn

... so that they are now composed of individual blocks. That way, when a
grid location is hit, we can easily draw the cell as hit and not draw
the entire ship as a monolithic block. It also facilitates a way of
checking whether a ship has been destroyed. Now, if a ship is sunk, the
'sunk' parameter is sent to the enemy game server on the next turn. Why
the next turn? Because that is the first oppurtunity to send JSON to the
enemy game server