Track opt-out ratio

There is not preference history data, so we store daily
counts in an intermediate table and query that table to build
the tsv files.

Change-Id: I697f5db6124d6ddccc2b97680b20fb5d4797488e
Mingle: https://wikimedia.mingle.thoughtworks.com/projects/multimedia/cards/735
Merge "Track opt-out ratio"