Allow Financial Types to be specified for Discount options

When a discount set is specified, each fee level in it needs to have a Financial Type associated with it in the same way that a Financial Type is associated with each Event Fee in the quick config price set for the event.

At a UI level, this means that an additional column containing a field for Financial Type needs to be added to the right of each row in the discount set table (see attached image).

The financial type for each row needs to be stored in the civicrm_price_field_value.financial_type_id field for each of the price sets having price specified for that row.