git-gui: Skip nicknames when selecting author initials
Our blame viewer only grabbed the first initial of the git.git author string "Simon 'corecode' Schubert". Here the problem was we looked at Simon, pulled the S into the author initials, then saw the single quote as the start of the next name and did not like this character as it was not an uppercase letter.
We now skip over single quoted nicknames placed within the author name field and grab the initials following it. So the above name will get the initials SS, rather than just S.
Signed-off-by: Shawn O. Pearce <firstname.lastname@example.org>