SDL:Update XPM icon

Updates XPM icon so it's high quality.

Steps for making a icon - Requires GIMP:

1. Make sure the image you want to use is a 8-bit RGB 96x96 png.
2. Go to Image > Mode > Indexed and make sure everything is exactly as it follows.
3. Go to File > Export as(or Shift+Ctrl+E) and make sure it's a XPM file with these settings
4. After exporting the XPM file, you will want to edit in a text editor so the second line is like this. const char * SDL_icon_xpm[] = {

After that, just clean and compile, also included the png used for reference.