Add new messages for article and image attribution
The new renderer will pull these messages from the wiki so that they
can be customized there.
Relies on:
Change-Id: Ifd80ca8c9b4f44100506fd52daa98093f88f0b5e
(cherry picked from commit 4f60b4ef561a855299f509d5a7d9f091e41853a8)