Added jQuery image popup support

Lot of things have been done:
1. Used Clapper's Octopress image popup plugin.
2. Disabled comments in "About" and "Categories".
3. Modified the contents of some of my old pages and posts.
4. Created `/stylesheets/print.css` for printer-friendly styles. For
example:
    - Black hyperlinks
    - Hide the navigation bar and the sidebar
    - Reduce the margin of headings
    - Hide the comments
5. Corrected the paths of some image files