Show average reviews per day
Show average reviews per day

Show average reviews per day across all reviewers as well as across the
core review teams.

Change-Id: I73cb6359d4f256c097c555b9b79d375042877cb7

JohnGarbutt/reviewstats,openstack-infra/reviewstats,JohnGarbutt/reviewstats,cp16net/reviewstats,openstack-infra/reviewstats,cp16net/reviewstats