Added applyTransformation to TextureMap

The method is called just before it's passed to ``TextureAtlasSprite``.

Use case (http://puu.sh/b9gzG.png don't mind the odd colors, it's an odd texture pack):
```
	@Override
	public BufferedImage applyTransformation(BufferedImage image) {
		for (int y = 0; y < image.getHeight(); y++) {
			for (int x = 0; x < image.getWidth(); x++) {
				int color = image.getRGB(x, y);
				int alpha = (color >> 24) & 0xFF;
				alpha *= ConfigurationHandler.alpha;
				color = (color & 0x00FFFFFF) | (alpha << 24);
				image.setRGB(x, y, color);
			}
		}

		return image;
	}
```