Split Product rule in Marketing

[bjarnef]

At the moment there is a "Product rule" in Marketing section, which says "No product or product category selected" when none has been selected. At the moment this allow to pick any node in the content tree and only a single node per rule.

I think it would make more sense to split this into a "Category" and "Product" rule, to select one or more categories or products.

This picker could also be replaced with re-use of the core tree pickers.