Update all the things! _o/

 * All projects have been updated to pull from their official GitHub/etc
   repositories. ('bout time everyone got off those SVN servers! :p )
 * Goodbye ancient Skulltag and your special version of FMOD!
 * This overlay does not contain any ports that work with doomseeker,
   but doomseeker is still there anyway.
 * SLADE still doesn't work. :p