Add "store per language variation" support

[MichaelNielsenDK]

If you turn on "Allow vary by culture" on the Store Picker, you'll get the yellow box with the message:

Unable to locate an associated Store for this product. Please make sure you have added a Vendr Store Picker to your content root node. on all products.

The store is picked on the root node. I've also tried removing and adding the store again, but that did not help.

Umbraco 8.11.1 Vendr 1.5.1