Add new library oslo.i18n

Add the new library oslo.i18n so projects can start adopting it.

This is needed to backport oslo.utils which is needed for
python-keystoneclient.

Partial-Bug: #1357652

Conflicts:
        global-requirements.txt

Change-Id: I65c44627dc1163d15962edef575134fb7c857a2e
(cherry picked from commit 977e7fc0852e58bc77c3db8bfdb70fbb17c50cb3)
(cherry picked from commit 352a88ecf92806a97668acb8b248658e36095ea4)