Create Configuratie entity.
Create configuratie GUI.
Refactor away duplicate code in OfferteArtikel requests.
Refactor away duplicate code in OfferteArtikel requests.
Refactor away duplicate code in OfferteArtikel requests.

Forgot to commit this file.
Refactor Artikel extra prijs to extra prijs van toepassing.
Implement extra prijs calculation.
Display extra prijs in offerte gui.
Merge pull request #6 from Tactics/extra-prijs

Extra prijs