[REF] changes suggested by @guewen

Set a keyword argument on the context to better respect the convention.
Make it clear in docstrings that the side-effects on field_names are
intended.
Allow the context to contain iterable types supported by the ORM.
Merge remote-tracking branch 'team/7.0-add-stock-available' into 7.0-_prod-conflicts

Conflicts:
	stock_available/product.py