Improve payment and shipping methods

[SamBrishes]

• [ ] Payment: Provide payment options / payment method
• [ ] Payment: Support "negative fees", ex. to offer a discount on invoice
• [ ] Shipping: Additional Option "Supports Shipment Tracking" / "Shipment Tracking URL scheme"
• [ ] Shipping: Additional Option "Insured shipping up to [amount]"
• [ ] Shipping: Additional Option "VAT / Taxes rate results from order" *
• [ ] https://github.com/OFFLINE-GmbH/oc-mall-plugin/issues/920
  • [ ] New rule / condition handling
• [ ] https://github.com/OFFLINE-GmbH/oc-mall-plugin/issues/826
  • [ ] New rule / condition handling
  • [ ] Limit visibility of Payment Methods (Either directly public/private or via CustomerGroup)

* In Germany, the tax rate for shipping costs is calculated on the basis of the products to be shipped. In the case of an order with different tax rates (7% and 19%), this is calculated proportionally based on the total. See Mehrwertssteuer auf Versandkosten (german article) / Umsatzsteuer auf Versandkosten (german article)

[SamBrishes]

Thinking about new condition-based handling, at least for payment / shipping methods

if [condition] then [action]

Available conditions

• cart [contains] list
• cart total [greater|lower] amount
• cart weight [greater|lower] amount
• cart number of items [greater|lower] amount
• shipping country|region [in|not-in] list<country|region>

Available Actions

• enable|disable method
• set specific price (shipping) | set specific fee (payment)
• set guaranteed days to delivery (shipping)
• increase amount of parcels/packages (shipping)