LP#1684126: copy images used by staff portal outside of /xul/

LP#1684126: copy images used by staff portal outside of /xul/

This patch ensures that various images used by the web
staff client will remain available whenever the last bits
of the XUL client are removed.

To test:

[1] Apply patch
[2] Verify that all of the images on the web staff client's
    splash page are displayed.
[3] Retrieve a patron that has an alertable condition (e.g.,
    the patron record is expired. Verify that the stop sign
    image is displayed.

Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>
Signed-off-by: Ben Shum <ben@evergreener.net>