Bug 26621: Adjust .mailmap to reduce the number of invalid authors

Bug 26621: Adjust .mailmap to reduce the number of invalid authors

This file is a nightmare, really. We should simplify it and order it correctly.
Letting it here for now, I'd like to run the gitstats command on it to double check the output.

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
JD: Amended patch: remove dup occurrences for Brendan

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit 122a2c58ff61c831b9de633ed01a6986fabaa7b0)
Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>