Parse and display commit authorship date in Git in Diffusion
Summary: Fixes T8826. Git tracks an "author date", which may be different from the "committed date". We don't currently extract/show this; do so.
Test Plan: {F1059235}
Reviewers: chad
Reviewed By: chad
Maniphest Tasks: T8826
Differential Revision: https://secure.phabricator.com/D14995