LP#1879983: UI for claiming staging

LP#1879983: UI for claiming staging

This patch adds a "Staging Staff" column to the To Be Staged
staff and buttons to allow staff to claim and release claims
of responsibility to handle staging an appointment.  A staff
member can take over another's claim, but will be asked to
confirm that they want to do so.

Also, reduces the freshness check interval on the to be staged
tab to five seconds, since if the curbside operations require
that staff claim appointments to stage in the first place, there
may be multiple computers in play displaying the to be staged tab.

Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>