Add an initial .mailmap

What does this MR do?

Add an intiail ".mailmap" file to better map users names and email adresses for git shortlog and git check-mailmap to work better.

Are there points in the code the reviewer needs to double check?

The reviewer can try git shortlog -nse with and without the ".mailmap" to see the difference.

Why was this MR needed?

It starts to make git shortlog and git check-mailmap useful.

What are the relevant issue numbers?

I don't know of any. I searched for "mailmap" and found nothing.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

I can add an entry into the CHANGELOG but this is for developers only so I am not sure it is really needed.

• CHANGELOG entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together