Allow saving lint errors to database

Summary: This saves lint errors to the path change of current commit. It requires pushed revision. It doesn't save difference from previous commit mentioned in T2038#comment-4 - I don't plan doing it after all, everything would be much more complicated and the amount of data saved with this approach isn't that bad.

Test Plan: Applied patch, ran script, verified DB.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2038

Differential Revision: https://secure.phabricator.com/D3899