add simple web services for adding or subtracting records from a temp list

add simple web services for adding or subtracting records from a temp list

GET /eg/opac/api/mylist/add?record=45
GET /eg/opac/api/mylist/delete?record=45

The JSON response is a hash containing a mylist key pointing to the list
of bib IDs of contents of the temporary list.

The record parameter can be repeated to allow adding or removing
records as an atomic operation. Note that this change also now available
to /eg/opac/mylist/{add,delete}

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