Network Anniversary Insight. Fixes #1514

New network anniversary insight (#1514). It works as the following example:

Happy Twitter birthday! 5 years ago today, you joined Twitter, and since then you've put out 84 characters, 140 (or fewer!) at a time. It's likely you've spent about 3 hours and 3 minutes tweeting in those 5 years. You've asked your 7 followers 1 question. And 67% of your tweets have smileys in them! That deserves one more. :)