add ItemStack to/from NBT helpers (#202)

to simplify the "stackSize" NBT tag workaround

src/main/java/appeng/helpers/ItemStackHelper.java

@@ -0,0 +1,30 @@
+package appeng.helpers;
+
+import net.minecraft.item.ItemStack;
+import net.minecraft.nbt.NBTTagCompound;
+
+/**
+ * Methods to help with the added "stackSize" NBT tag to get around "Count" being written and read as a byte.
+ */
+public class ItemStackHelper {
+    public static ItemStack stackFromNBT(NBTTagCompound itemNBT) {
+        ItemStack is = new ItemStack(itemNBT);
+        if (itemNBT.hasKey("stackSize")) {
+            is.setCount(itemNBT.getInteger("stackSize"));
+        }
+        return is;
+    }
+
+    public static void stackWriteToNBT(ItemStack is, NBTTagCompound itemNBT) {
+        is.writeToNBT(itemNBT);
+        if (is.getCount() > Byte.MAX_VALUE) {
+            itemNBT.setInteger("stackSize", is.getCount());
+        }
+    }
+
+    public static NBTTagCompound stackToNBT(ItemStack is) {
+        NBTTagCompound itemNBT = new NBTTagCompound();
+        stackWriteToNBT(is, itemNBT);
+        return itemNBT;
+    }
+}