gitscraper: Provide way to get timestamps for files.

When scraping files from the repository allow passing an additional list of
files for which the timestamp of the last change is retrieved. Since this is
slow (the log needs to be traversed, since a blob doesn't know about commits
its referenced by) only specified files get this retrieved.

Change-Id: I61a2ef812ac18ffb5898c01ce070046d4ca00a15
1 file changed