ajaxified marking  attendance. officer photo bug fix. slider images.

Made ability to sign up for an event more visible. If user is already signed up already, clicking the signup button will redirect to an edit signup page. Users can mark other users as having attended. When a user has been marked as attended the event page will update via ajax.

Fixes to office portrait bug caused by event posts pushing down officer portraits.
https://ieee.berkeley.edu/about/officers

Added slideshow images from 2012.