[#2196] Use git blame line info for aggregate blame author modified and date info

[logical-1985516]

Fixes #2196

Proposed commit message

Uses blameLine to abstract away the string wrangling and improve
understandability. Magic numbers are also replaced to improve code
quality.

In order to use blameLine however, it is also changed to use 
author-time instead of commit-time, as there is a discrepancy
between the two, causing some test cases to fail.

The naming of the timestamp field in GitBlameLineInfo is changed
to reflect that it is in seconds, as author-time is in seconds.

Other information

Surrounding code which states milliseconds is also changed to state seconds correctly, as this PR is meant to resolve a code quality issue anyways. If this is not ok, I can revert the last commit.

[logical-1985516]

Hi, I have noticed that some test cases take a very long time to finish. Could this be due to the additional overhead incurred from running git blame command in blameLine?