* Update - deposits and coupons interactions refactored.
* Fix - Deposits discounts are tracked by core.
* Fix - Correctly close output buffering if already called before.
* Fix - Disabled payment gateways are available for payment plan orders
* Fix - Partial payments going into processing status instead of partial-payment status.
* Fix - Only step by whole numbers in plan amounts.
* Fix - Correctly calculate discounts for items in cart with count bigger than one.
* Tweak - More prominent payment link in customer invoice.
* Fix - Wrong coupon amount for future payments.
* Fix - 1 cent calculation error in discount applied toward future payments.
* Fix - Tax amount not divided proportionately when prices are displayed exclusive of tax.
* Fix - Wrong coupon discount amount for prices entered exclusive of tax.
* Fix - Original order Future payments value changes after Issuing Remaining Invoice.
* Fix - Future payments calculated incorrectly with coupons and prices inclusive tax.
* Fix - 1 cent calculation error in total and subtotal.
* Fix - get_future_payments_amount mixes price with tax with discount without tax.
* Fix - Coupon amount is multiplied when multiple deposits are in cart.
* Fix - All orders going to Partially Paid, even if there's no deposit on them.
