Attempt to add Disqus comment count

Per instructions at http://help.disqus.com/customer/portal/articles/565624
Remove #disqus_thread from href
Assign value of ${post.id} to data-disqus-identifier
Use protocol-relative URL syntax to fetch Disqus JS
Add css to show comment icon on blog index page

Also, updated iconsprite with latest version which includes the icon
itself.
Add comment count to blog post page
Merge pull request #339 from spring-io/comment-count