Bug 7291: Adds new field aqbooksellers.deliverytime

Bug 7291: Adds new field aqbooksellers.deliverytime

New field deliverytime in aqbooksellers table. It is an estimated
delivery time for orders (in days).
You can set this delay on the supplier modification page.
It is used in the late orders search.

The order estimated date is the aqbasket.closedate +
aqbooksellers.deliverytime

If you set a delay, the query check if closedate <= today - delay

If you set a "delivery time from" and a "delivery time to", the query check if
$delivery_time_from <= aqbooksellers.deliverytime is not NULL and if
closedate + deliverytime >= $delivery_time_to
if there is not a time_to then $delivery_time_to = the current date.