Rename /old/ to /classic/ (#822)

https://github.com/privacytoolsIO/privacytools.io/pull/820#issuecomment-479334000

_includes/sections/resources.html

@@ -51,4 +51,4 @@
   %}
 
 </div>
-<p><a href="/old/">Prefer the old site?</a></p>
+<p><a href="/classic/"><i class="fas fa-info-circle"></i> Prefer the classic site? It's still around!</a></p>

pages/old.html

@@ -1,6 +1,6 @@
 ---
 layout: default
-permalink: /old/
+permalink: /classic/
 ---
 
 <div class="alert alert-warning" role="alert">