LP#1715767: Allow others to use my account (privacy waiver)

LP#1715767: Allow others to use my account (privacy waiver)

Use case: Jane Doe has a hold ready for pickup but is unable to come
into the library.  Her husband John Doe goes to the library to pick up
the hold on her behalf.  His name is listed on Jane's account, so
library staff know it's okay to check out the book on Jane's account and
give it to John.

This commit adds a new table which lists the names of people who are
allowed to place holds, pick up holds, check out items, or view
borrowing history for a user account.  Staff can add, edit, or remove
entries via the patron editor in the web client; patrons can do so in My
Account.  The entries are not linked to other user accounts and they do
not add any extra functionality.  They are essentially special patron
notes for circulation staff.

Signed-off-by: Jeff Davis <jdavis@sitka.bclibraries.ca>
Signed-off-by: Chris Sharp <csharp@georgialibraries.org>