v0.2.10-b1

Added ENPA appendix charts: xsar, users with exposure notifications
Changed how SAR% is charted: one graph per category, showing +/- one standard deviation
Try to make bounds on SAR% more sensible.
Changed the offset for SAR to 7 days
Exclude iOS ENPA data before Feb 24th, 2021
Allow using 28 day rolling averages