Bug 6867: Date last seen ignored on import

Bug 6867: Date last seen ignored on import

The date last seen field (952 $r) and replacement price date (952 $w) were being
ignored on import, being replaced with NOW() as a hardcoded value.  This patch will
allow a value to be imported, but if none is, it will use the ISO date of import
as a default.

Signed-off-by: Nicole C. Engard <nengard@bywatersolutions.com>
Signed-off-by: Ian Walls <ian.walls@bywatersolutions.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>