Import Python six v1.4.1.

Python six just consists of a single Python file, so this includes
the file as a convenience.

Change-Id: I98ed50fba657013f5f3f12a4d13b3ba5558bfa2e
Reviewed-on: https://gerrit.libreoffice.org/6687
Reviewed-by: Michael Stahl <mstahl@redhat.com>
Tested-by: Michael Stahl <mstahl@redhat.com>