Quantity to one, and minimum items fields.

-"quantity_invoice_one" field in view and database(item_period)
-Pluggin created: SetQuantityToOneTask when invoicing
-"min_items" field in view and database(item_dependencies). It can be
positive just when item_id = child_item_id. Otherwise set to 0.
	*It has been added into checkDependencies method in 	webServicesSession
-Database backup with new fields and data. (older ones deleted)