Only show the coupon number if nfe is not active

When the user has both the ecf and nfe plugins active, display the invoice
number instead of the coupon number in the sale details.

Change-Id: I2d1d99ec0e8aa4be2f9f28838aac6d8e3999c332
(cherry picked from commit ffdf35c50def141df63d5178231b33720d52d594)