A rentable is a period during which a InventoryObject can be rented.
A InventoryObject can have multiple rentables, each representing
different configurations (type, tags, pet policy, for rent, etc...)
of the same physical accommodation. This exists because it's typical
for holiday parks to upgrade accommodations.
When changing validity of rentables, note that other rentables might become
inactive due to this change. A InventoryObject cannot have more than one
active Rentable for a given date.