Converted SVGs to PNGs for Internet Explorer compatibility

The game's SVGs are now converted to PNGs, and the PNGs are used
by the game. With this, the game is finally compatible with
Internet Explorer, while the compatibility is preserved with
other browsers.

	new file:   bird.png
	new file:   birdcage.png
	new file:   csaj.png
	new file:   ground.png
	new file:   guard.png
	new file:   kecskecsaj.png
	modified:   shapeshift.js