Added list.reversed() unittest

test/unittest/list_reversed.gravity

@@ -0,0 +1,10 @@
+#unittest {
+    name: "List reversed.";
+    result: "[4,6,1,2,4]";
+};
+
+func main() {
+  var list = [4, 6, 1, 2, 4]
+  var reversed_list = list.reversed() //[4,2,1,6,4], list remains unmodified
+  return list.String()
+}