Shelve work on retention.py
Switch to normal two-column layout

We were using a different method of doing columns on the charts page.
Drop back to the one we're using everywhere else so we can line up
charts the way we want.
Show week 0 on charts

Otherwise I won't be included in retention. :-)
Remove obsolete chart notes
Prune dead comment
Move retention.py to a json simplate
Let's see about doing folding client-side
Rough in the retention

Basically what we have in the spreadsheet.