Fix german translation of Default Purchase Unit of Measure

[SamuelHelbling]

Fix german translation of "Default Purchase Unit of Measure".
In version 15, “Standard purchase unit” is translated into German in the same way as “Standard sales unit,” which is confusing.

Is Purchase Item,Ist Einkaufsartikel,
Default Purchase Unit of Measure,Standard Maßeinheit Verkauf,
Minimum Order Qty,Mindestbestellmenge,
Minimum quantity should be as per Stock UOM,Die Mindestmenge sollte der Lagermenge entsprechen,
Average time taken by the supplier to deliver,Durchschnittliche Lieferzeit des Lieferanten,
Is Customer Provided Item,Vom Kunden angelieferter Artikel,
Delivered by Supplier (Drop Ship),durch Lieferanten geliefert (Streckengeschäft),
Supplier Items,Lieferantenartikel,
Foreign Trade Details,Außenhandelsdetails,
Country of Origin,Herkunftsland,
Sales Details,Verkaufsdetails,
Default Sales Unit of Measure,Standard Maßeinheit Verkauf,
Is Sales Item,Ist Verkaufsartikel,
Max Discount (%),Maximaler Rabatt (%),

In v16 it is correct: