Support different image formats for loading/saving

[bouwkast]

Right now I use the binary form of PPM cause it is dead simple to implement, but this means that I have the annoying task of taking an image and passing it through GIMP to first export as a PPM and then I can use it in the application. Then after the application makes it better I have to resend it through some photo editor (GIMP or Photoshop) to then export it into a format that normal people use.

Let's aim for a lossless format first (png maybe).