IE improvements

Microsoft does not support PNG images that well, and I _had_ used PNG images for almost everything. That was a very bad idea since I had used some hacks that fixed PNG support for Internet Explorer. I guess that being religious about something is pretty stupid, and I have now converted some pictures to GIF (those pictures that don't have to be transparent and anti-aliased). This has improved the rendering speed on IE dramatically...!

Apart from that, I now use my own PNG transformer. I may write an article about it.