CHANGE TO PREVIOUS .046 DATABASE UPDATE

CHANGE TO PREVIOUS .046 DATABASE UPDATE

This commit changes .046 updatedatebase , where itemnumber was changed
to int and keyed on items table.  As there is code in serials module that
uses itemnumber (text) as a list of itemnumbers, this change would cause data
loss if that field had multiple items in it.
Instead, we add a new table to link serial and items tables, so that
(1) we can have many items per serial issue, and
(2) staged upgrades that use the serial.itemnumber (text) list won't be affected.
Further commits will make use of the serialitems linking table.

Signed-off-by: Chris Cormack <crc@liblime.com>
Signed-off-by: Joshua Ferraro <jmf@liblime.com>