Tiling

I added the supports of tiles in the level editor which looks really nice. Tilling is available on all layer independantly. Tile format right now is square only based on 256 x 256 pixel put with a yummy auto-dectect spritesheet frame based on a left to right, top to bottom system. So this permits the user to create tiles 256x 256 pixel but he may put has many frame on the spritesheet that he wants and the system will automaticaly navigate in the pgn file est extract the frame within the spritesheet.

I also added the "Zoom" functionnality to zoom-in and out on the level the user is creating. I added this because even myselft when creating level wanted a more global view of the level (zoom out) and some times I really wanted to get close in for detail checkup.