Prorated billing for Contracts

Adding items to a contract mid-cycle should allow for the choice of prorated billing E.g

• Do not prorate
  Items are not prorated for partial periods (current functionality).

• Prorate and add to next invoice
  Adjust the item quantity for the next billing period and include the prorated amount as a separate line item on the next invoice.

• Prorate and generate standalone invoice
  Adjust the item quantity for the next billing period and generate a standalone invoice for the prorated amount.