Added a "time ago" display to the viewer's info box

(and also a bit of formatting ;-)

• For less than a week, we get "x days ago"
• For less than a month, it's "x weeks ago"
• For less than a year, it's "x months ago"
• For less than 5 years, it's "x years and y months ago"
• For more than 5 years, it's "x years ago"