Allow older version

  Add legacy installer
    
 Some people don't like the newer skitch. I'm one of them. So, I'll allow
 for an older version of skitch to be installed.
    
 See
    http://www.tuaw.com/2012/09/20/skitch-2-0-is-like-skitch-1-0-without-all-those-pesky-features/
   for some decent reasons why the new version isn't as awesome.