Chessmonk goes Cairo

I rewrote the board view widget to get rid of the dependency on GnomeCanvas, now it only uses GtkDrawingArea and Cairo. In the process I “cleaned up” the animation code by making it automatically figure out all required animations between two positions and added piece fading and (optional) coordinates for good measure. Here is a little screencast showing it in action, of course being a gif it is not of high quality: