add checkmark to the narbar of all constructed HTML

We added a checkmark all narbar's that has the make effect of
clicking on the **Nu HTML check this web page** link at the very
bottom.  This makes it much more convenient when one needs
to quickly check the HTML of a number of web pages.

Run `make www` to perform the above.

location.html

@@ -118,13 +118,13 @@
 </div>
 
 <!-- END: this line ends content from: inc/header.default.html -->
-<!-- START: this line starts content from: inc/navbar.default.html -->
+<!-- START: this line starts content from: inc/navbar.empty.html -->
 
 <div class="navbar">
-&nbsp;
+<a class="Right" href="https://validator.w3.org/nu/?doc=https%3A%2F%2Fioccc-src.github.io%2Ftemp-test-ioccc%2Flocation.html">&#x2713;</a>
 </div>
 
-<!-- END: this line ends content from: inc/navbar.default.html -->
+<!-- END: this line ends content from: inc/navbar.empty.html -->
 <!-- START: this line starts content from: inc/before-content.default.html -->
 
     <div class="content" id="content">