A .mailmap file is missing

Many contributors have set up their identity differently over time. Thus, OTB seems to have had 97 different contributors, but in reality, there were only 57. It would therefore be wise to add a .mailmap file in the root directory of the repository to better count and identify contributors.

Moreover, removing the ambiguity regarding the authors of the contributions would facilitate the subsequent and automated control of the signing of the CLA (contributor license agreement).

The last identity used by the contributor should be used as the reference identity in order to easily contact him if needed. As the identity permits to identify the author of a contribution, not its copyright holder, it doesn't matter if a contribution provided by "John Doe john.doe@xxx.fr" is later assigned to "John Doe jdoe@yyy.eu" in the log (as long as these two identities correspond to the same physical person).