Allow looking up recipes in JEI with non-item slots (#451)

src/main/java/appeng/container/interfaces/ISpecialSlotIngredient.java

@@ -0,0 +1,10 @@
+package appeng.container.interfaces;
+
+import javax.annotation.Nullable;
+
+public interface ISpecialSlotIngredient {
+
+    @Nullable
+    Object getIngredient();
+
+}