In backoffice forms for membership and contribution save receipt_text to the database so that IPN calls can use it

Currently the receipt_text entered in the back office is not saved in the DB.
This is a problem for a few reasons:
1) IPN calls cannot use it when the callback
Right now we hide the field if we think IPN will be used.
(BAD: Right now we assume it will be IPN if it is recurring)

2) For some payment processors we know the contribution status at different times:

• For IPN: much later
• For IATS: Immediately on form submit
• For Direct post type: Before we submit the form
  It is really difficult to be smart about hiding and showing the receipt text field when the user selects different payment processors. It would be better to always show it, store it, then use it when we know the payment is completed.
  Perhaps we will need a warning that the payment may not go out right away.