Generalize analytics support in default theme

As the number of privacy-preserving analytics options proliferates,
it no longer makes sense to support specific solutions provided by
ad-tracking corporations.

pelican/themes/notmyidea/templates/analytics.html

@@ -1,26 +1,3 @@
-{% if GOOGLE_ANALYTICS %}
-    <script type="text/javascript">
-    (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
-    (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
-    m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
-    })(window,document,'script','https://www.google-analytics.com/analytics.js','ga');
-
-    ga('create', '{{GOOGLE_ANALYTICS}}', '{{GA_COOKIE_DOMAIN if GA_COOKIE_DOMAIN else 'auto'}}');
-    ga('send', 'pageview');
-    </script>
-{% endif %}
-{% if GAUGES %}
-    <script type="text/javascript">
-    var _gauges = _gauges || [];
-    (function() {
-        var t   = document.createElement('script');
-        t.type  = 'text/javascript';
-        t.async = true;
-        t.id    = 'gauges-tracker';
-        t.setAttribute('data-site-id', '{{GAUGES}}');
-        t.src = '//secure.gaug.es/track.js';
-        var s = document.getElementsByTagName('script')[0];
-        s.parentNode.insertBefore(t, s);
-    })();
-    </script>
+{% if ANALYTICS %}
+{{ ANALYTICS }}
 {% endif %}