Don't automatically recalculate crafting plans

Instead, any time a change is made which invalidates a crafting plan,
update the visual display to show that the plan is out of date, and
add some extra affordances to recalculate.

src/client/site/craft_page/step/step.scss

@@ -53,4 +53,12 @@
             }
         }
     }
+
+    &.complete {
+        opacity: 0.25;
+
+        h3 {
+            text-decoration: line-through;
+        }
+    }
 }