Fix issue with Klarna fee disappearing when updating order in admin

When the order has a Klarna fee and is updated in the admin panel, the fee is removed. 

This is because neither the address or the selected payment option is available in `ModelTotalKlarnaFee` when called from the admin panel. 

This pull request changes how the information is retrieved to fetch the required information from the `POST` request instead. 

This issue has been verified in version 1.5.5.1 and this fix has been tested with that version.