LP#1879983: Restrict top-level curbside tab display

LP#1879983: Restrict top-level curbside tab display

Refactor the code checking for curbside-available current-pickup
libraries so that it is checked for all of MyOPAC, allowing us to hide
the Curbside Pickup top-level tab when there are no holds ready at
curbside pickup enabled locations.  The tab will always be at the end of
the list if it is visible.

Signed-off-by: Mike Rylander <mrylander@gmail.com>
Conflicts:
    Open-ILS/src/perlmods/lib/OpenILS/WWW/EGCatLoader.pm
    Open-ILS/src/templates/opac/parts/myopac/base.tt2

Signed-off-by: Jason Stephenson <jason@sigio.com>