Show time from now for messages, and exact date & time on mouseover.

NB: instead of the mouseover event using jquery, we could use the calendar() option of moment.js, which shows "Today/Yesterday/last Monday at 2:30 AM" for the past 2 weeks, but for earlier date it only shows the date without the time: "7/06/2014". This would then have to be customised:
time: -> moment(@createdAt).calendar()