refactor templates layout

@see https://gohugo.io/templates/new-templatesystem-overview/

layouts/_partials/copying.html

@@ -0,0 +1,14 @@
+{{ "<!--" | safeHTML }}
+   {{ .Site.Title}} - {{ .Site.Params.tagline }}
+
+   This page was created by {{ fmt.Printf "%s <%s>" .Site.Params.Author.name .Site.Params.adminEmail | safeHTML }}.
+   The date of creation and last modification should be available within the page
+   below.
+   
+   Unless stated otherwise, and to the extent possible under law, the author has 
+   dedicated all copyright and related and neighbouring rights to this content 
+   to the public domain worldwide. This file is distributed without any warranty.
+
+   See <http://creativecommons.org/publicdomain/zero/1.0/> for
+   a copy of the CC0 Public Domain Dedication. 
+{{ "-->" | safeHTML }}