VID-2028 tracking rendered media in ranges

After this change goes to production we'll see 5 lines in grafana (http://graph-s3.wikia-prod/grafana/#/dashboard/db/Liz%20Dash), each representing the time it takes to render a given range of media. Ranges are 0 => 1-20, 1 => 21-40, 2 => 41-60, 3 => 61-80, 4 => 81-100.