LP#1190508: Rename certain image files to avoid Ad Block Plus's blacklist

Ad Block Plus was blocking images with /images/adv_ in their pathname. It is
presumed that "adv" was short for "advertisement".  I have renamed the files
and the references to avoid the ABP blacklist.

Signed-off-by: Dan Pearl <dpearl@cwmars.org>
Signed-off-by: Kathy Lussier <klussier@masslnc.org>
Signed-off-by: Ben Shum <bshum@biblio.org>