Improve shipment tracking

[Michael-Herzog]

At the moment, you always have to add the tracking URL for each shipment, even though it never changes.
It should be possible to save these URLs somewhere (including placeholders, e.g. for tracking numbers, which are then resolved).
Perhaps directly with the shipping method.

The PayPal system name for the shipping service could also be saved there.
This is the only way to ensure reliable matching at PayPal and to enable more PayPal functions.

[mgesing]

At the moment, you always have to add the tracking URL for each shipment, even though it never changes.

Don't reinvent the wheel, See IShipmentTracker and #1149.

[Michael-Herzog]

I already had in mind to take a closer look at this. When looking at this issue. But of course it's better to write i down where it belongs: in this issue.