Fix for tax display in case of any discounts applied

The hidden tax amount was missing for the subtotal_incl_tax and tax display of each row. The subtotal was correct but has been changed to also use row_total like subtotal_incl_tax uses row_total_incl_tax.
Merge pull request #128 from RobM84/patch-1

[~BUGFIX] Fix for tax display in case of any discounts applied