Add Git mail mapping

Added a Git mailmap (1) file to link to in documentations to allow
contributors to send mails regarding security issues.
This prevents unnecessary overhead of updating all documents when new
core team and members and contributors are added and additionally adds
the main functionality of the file: Mapping commits when someone uses a
different email address.

References:
  (1) https://git-scm.com/docs/git-shortlog#_mapping_authors

Epic: GH-8
Resolves GH-10

.mailmap

@@ -0,0 +1,14 @@
+# Copyright (C) 2018-present Arctic Ice Studio <[email protected]>
+# Copyright (C) 2018-present Sven Greb <[email protected]>
+#
+# Project:    Styleguide JavaScript
+# Repository: https://github.com/arcticicestudio/styleguide-javascript
+# License:    MIT
+
+# Configuration for Git mail mapping feature to coalesce together commits by the same person in the shortlog,
+# where their name and/or email address was spelled differently.
+#
+# References:
+#   https://git-scm.com/docs/git-shortlog#_mapping_authors
+Arctic Ice Studio <[email protected]>
+Sven Greb <[email protected]>