fixed pipes not being marked as changed when they do

closes #153

src/main/java/de/ellpeck/prettypipes/misc/ItemFilter.java

@@ -129,6 +129,7 @@ public class ItemFilter extends ItemStackHandler {
     public void save() {
         if (this.modified) {
             this.stack.getOrCreateTag().put("filter", this.serializeNBT());
+            this.pipe.setChanged();
             this.modified = false;
         }
     }

src/main/java/de/ellpeck/prettypipes/pipe/PipeBlockEntity.java

@@ -65,6 +65,11 @@ public class PipeBlockEntity extends BlockEntity implements MenuProvider, IPipeC
         public int getSlotLimit(int slot) {
             return 1;
         }
+
+        @Override
+        protected void onContentsChanged(int slot) {
+            PipeBlockEntity.this.setChanged();
+        }
     };
     public final Queue<NetworkLock> craftIngredientRequests = new LinkedList<>();
     public final List<Pair<BlockPos, ItemStack>> craftResultRequests = new ArrayList<>();