Bug 31631: (follow-up) Use CalculateFundValuesIncludingTax when modifying existing...

Bug 31631: (follow-up) Use CalculateFundValuesIncludingTax when modifying existing order

This patch depends on Bug 31840.

To test:
1) Edit an order and increase the price so that you would expect it to
trigger a warning that you will exceed the amount allowed for this Fund
2) Confirm the warning is triggered

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>