changed icon for freezer ( issue #614 ), for rope (to be easier to recognize) and cluster bomb (to be easier to recognize and to so that it can be distinguished from the regular grenade's icon even when no color is present or perceived

foreach(dir "Fonts" "Forts" "Graphics" "Locale" "Maps" "Music" "Sounds" "Themes" "Missions" "Names" "misc" "Scripts")
  add_subdirectory(${dir})
endforeach(dir)