First mostly successful pass

This is the most straight forward approach. Serial execution using
callbacks all the way down. There is some ugly stuff here. The pocket results
need to be sorted inline. The spreadsheet rows are added individually and
uses an async counter. The row adds are not serialized and can potentially
be added out of order due to race conditions.
A little cleanup and adding a few comments
Added tests

Added a test file that attempts to exercise the backfill script
in isolation. All dependencies are mocked and injected. The script will
run offline. Right now the test file is one complex test run. There is
no harness, several mixed assertions, and only the happy path is tested.