Weekly stats

With the first full month of stats in the bag it's time to add weekly stats (and yes, you can guess what my next branch will do... I just wanted to get this one out, first) :-)

The other things that I really need to do is work on
- configurability and cookies to store things (what's the first day of the week? metric anyone?
- localization
- authentication (I wanted to do that weeks ago and got sidetracked)