Add .mailmap: fix duplicate/wrong e-mail or name in commit log

It will be reused form generate AUTHORS file

Change-Id: I43c388df34551b898f15913c2625b1996ace0cbc
Reviewed-on: https://code.wireshark.org/review/5841
Petri-Dish: Alexis La Goutte <alexis.lagoutte@gmail.com>
Reviewed-by: Lukas Emersberger <lukas.emersberger@gmail.com>
Reviewed-by: Michael Tüxen <tuexen@wireshark.org>
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>