[slapos_web] Improve invoice list section

- Show float with 2 digits after . only
- Don't list reversal Sale Transaction Invoices, this only leads to confusion
- Show Payment State as Cancelled if a Reversal Sale Invoice Transaction is started for the Pending account (it means Payment was cancelled).

- List Invoices in Reverse Order (start date), so it is easy to identify if you have something pending to Pay.