webstaff: some images are coming from /xul/server/...

A handful of images in the web staff client are being drawn from /xul/server/skin/media/images:

circ/patron/t_alerts.tt2: <img src='/xul/server/skin/media/images/stop_sign.png'>
circ/patron/t_xact_details.tt2: apply manual columns, see xul -->
t_splash.tt2: <img src="/xul/server/skin/media/images/portal/logo.png"/>
t_splash.tt2: <img src="/xul/server/skin/media/images/portal/forward.png"/>
t_splash.tt2: <img src="/xul/server/skin/media/images/portal/back.png"/>
t_splash.tt2: <img src="/xul/server/skin/media/images/portal/retreivepatron.png"/>
t_splash.tt2: <img src="/xul/server/skin/media/images/portal/bucket.png"/>
t_splash.tt2: <img src="/xul/server/skin/media/images/portal/bucket.png"/>
t_splash.tt2: <img src="/xul/server/skin/media/images/portal/helpdesk.png"/>
t_splash.tt2: <img src="/xul/server/skin/media/images/portal/helpdesk.png"/>
t_splash.tt2: <img src="/xul/server/skin/media/images/portal/reports.png"/>

These images should be copied elsewhere and the links updated as part of making it possible to do a "git rm Open-ILS/xul" in the future.

Evergreen master