dev/cividiscount#5: Add Taxes to Membership Amount After Discount
Created by: MiyaNoctem
When creating a membership, if you apply the discount code after selecting the membership, the total amount will be discounted, but will fail to include taxes.
Issue tracked here: https://lab.civicrm.org/extensions/cividiscount/issues/5
If discount was applied after selecting membership type, total amount was calculated by applying the discount to original membership type minimum fee, but no taxes where added.
Fixes the total amount by calculating tax and adding it, if membership type has related tax rate.