Fixed handling of (l)enums in product sync

As the SPHERE API does not allow to set the labels of (l)enum typed attributes, we do patch the attributes before comparing them.
This patching works also smart within a create-or-update workflow.

The difference in JSON:
before:

{ "name": "color", "value": { "label": "Black", "key": "black" } }

now:

{ "name": "color", "value": "black" }