UI refinement.

1. make the sidebar font bold for tags/categories page.
2. Prefer 'Droid Sans Mono' for post tags when available.
3. make the header supscript font grey for tags/categories page.
Load disqus comments manually.

For technical details, check
http://blog.yjl.im/2012/04/let-your-readers-decide-when-to-load.html .