Add .mailmap file

We've had a couple of different email addresses from the same person.
Coalesce them so they appear as one in the shortlog.

Change-Id: I4ff59fe5c32a5bf874ba829d9039ff80788d5b44
Reviewed-on: http://gerrit.causes.com/44342
Tested-by: jenkins <jenkins@brigade.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>