Smaller images + permissions fix

I converted almost all of the gif files to png in order to make them smaller. The only one that remains is the animated gif. I tried making an APNG that was smaller but failed. I modified the .css file to reflect my changes.

There seems to be a visual glitch in GitHub that shows the new png files as having no alpha. This is incorrect. The files still contain alpha information.

I also removed the EXIF metadata. The only thing it said was "Made by GIMP"

I also fixed the file permissions by doing chmod 0644 * in the directory.