Switch to astypedef, adds unit tests

Scripts/Interfaces/Item.astypedef

@@ -0,0 +1,7 @@
+type Item {
+    const constString& Name { get const; };
+    ItemCategory Category { get const; };
+    BattleItemCategory BattleCategory { get const; };
+    int Price { get const; };
+    bool HasFlag(const constString &in flag) const;
+}