Refactored inclusion of disqus script

- Added ARIA setting `aria-live="polite"` to comment output
- Removed duplicate <div id="disqus_thread"> from page/post templates
- Moved blocking JavaScript loading to the end of the document body.
- Merged JavaScript code for index and pages/posts using conditionals
- Moved global JavaScript disqus variables into the anonymous function to stop pollution of global namespace

.themes/classic/source/_layouts/default.html

@@ -9,6 +9,7 @@
     </div>
   </div>
   <footer>{% include footer.html %}</footer>
+  {% include disqus.html %}
   {% include google_analytics.html %}
   {% include google_plus_one.html %}
   {% include twitter_sharing.html %}