LP#1879983: Add curbside subtab to the My Account holds UI

LP#1879983: Add curbside subtab to the My Account holds UI

This updates the public catalog My Account holds tab to add
a subtab for curbside appointments. This subtab is displayed
only when the patron has available holds on the shelf at pickup
libraries that have enabled the circ.curbside library setting.

From this subtab, patrons can:

* Set times for curbside appointments and specify notes.
* Modify and cancel appointments.
* Mark themselves has having arrived at the library.

In addition to Mike Rylander, significant contributions to this
patch were made by Galen Charlton.

Sponsored-by: PaILS
Signed-off-by: Mike Rylander <mrylander@gmail.com>
Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>
Signed-off-by: Michele Morgan <mmorgan@noblenet.org>