Adding thumbnail image for screenshot

Signed-off-by: Matt Bernhardt <mjbernha@mit.edu>
Adding unbox_tabs post type, which will carry the front page content.
Adding unbox_card widget type, which will display links to slideshows.
Addding front-page.php, using fields defined in unbox_tabs post type.

Signed-off-by: Matt Bernhardt <mjbernha@mit.edu>
Lots of style changes to push the presentation closer to what Ilavenil has mocked up.

Signed-off-by: Matt Bernhardt <mjbernha@mit.edu>