input validation for showfeaturednews-template

- since sometimes news items don't have images, and you can't
  put <script> tags inside of templates, I created a conditional
  for the image which displays a nonexistent image with an onerror
  that hides the parent element. Ultimately, we'll be using another
  template in cases where this could possibly happen, but I'm
  leaving it this way for the main showfeaturednews-template because
  it's not hurting anything (and it will prevent future news items
  that don't have images from appearing).

Signed-off-by: William Rockwood <wrockwood@tadl.org>