AuthorDate instead of CommitDate for better accuracy of work hours estimate

[ehtec]

I believe the AuthorDate should be used instead of the CommitDate for the hours estimate. Otherwise, a rebase (for example) would reduce the work time drastically because all commits are committed at the same time (and potentially by the wrong person, I believe it makes more sense to assign the time to the Author instead of the person who rebased).

https://stackoverflow.com/questions/11856983/why-is-git-authordate-different-from-commitdate