0731b07d27
Start storing the duration of animations and videos in the `duration`
field on the media_assets table. This had to wait until 3d30bfd69 was
deployed, which had to wait until Postgres was upgraded in order to add
the duration column to the media_assets table without downtime.
Also add a fix script to backfill the duration on existing posts. Usage:
TAGS=animated ./script/fixes/079_fix_duration.rb