Select a Zone and allow management of its tax rate.
There is always only 1 active TaxRate per Zone (that is with a startDate and no stopDate).
When creating a new Tax rate, be able to enter the startDate, the rate and optionally an stopDate.
If there is already an active Rate, close it (set its stopDate to the day before the startDate of the newly created Rate).
Any rate can be edited but validation ensures that it's not possible to have rates that overlap.
#3 : UI is available for Tax rates but update for existing tax rates …
…must still be implemented
#3 : management of Tax rates is now fully working