feat!: quiqqer v2

See merge request !27

BREAKING CHANGE: quiqqer v2 has been renamed to quiqqer/core. a new major version will be created here so that we can still develop for both versions.

feat: shipping cost extended

See merge request !8

* Implemented new ERP Entity Interface
* Extension of standard shipping costs: consider country of customer
  * Now when the address is changed AND the default shipping cost is assigned, the default shipping price will be adjusted accordingly