LP#1570072: update hold notification methods upon preference changes

LP#1570072: update hold notification methods upon preference changes

This patch adds a feature where if a patron's hold notification
preferences are changed, they are given an opportunity to have
notfication methods for their pending hold requests updated to
reflect their new prefernces.

This feature affects both the public catalog My Account interface
and the staff patron registration form. In both cases, the user
is presented with a modal (staff-side) or interstitial page (public
catalog) asking them whether to update current hold requests.

Sponsored-by: MassLNC
Additional-work-by: Mike Rylander <mrylander@gmail.com>
Additional-work-by: Galen Charlton <gmc@equinoxinitiative.org>
Signed-off-by: Cesar Velez <cesar.velez@equinoxinitiative.org>
Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>