Faster comment search

At the end of the semester in Fall 2013, there were over 5000 comments written by 6.005 staff and volunteers.  We are still loading all 5000 of these (via ajax), but we do not load the extra information about this comment (i.e. the chunk line where this comment was written originally) until the user needs it.  This cuts comment load times by a factor of 20 (from ~6.5 minutes to ~20 seconds).