Bug 5263 - Add support for including fields from the ISSUES table in advanced due...

Bug 5263 - Add support for including fields from the ISSUES table in advanced due notices

Adding support for including fields from the Issues table in advanced due notices.
This is primarily to allow the inclusion of the due date for each item in the
advanced due notice, but will allow the inclusion of any field from the ISSUES
table.

This also adds code to exclude timestamp fields as these are irrelevant to the
end user in this context.

Note: Documentation should be updated to reflect the availability of the additional
fields in all circulation notices.

Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>