Link checksums differently from now on
    
    Change:
    - There are some checksum files which have the same names both for
      images and iso artifacts. Historically, we picked one (usually
      favoring ISOs I think), and the other got dropped.
    - Instead of doing that, just import all of them, separated into iso and
      images subdirectories. For the editions we show on getfedora.org,
      include both (image and iso) checksum files on the security page when
      appropriate.
    
    Signed-off-by: Rick Elrod <rick@elrod.me>