Add product restrictions to CMS standard product Search

This has been done for CSG as a custom search report and works really efficiently.

Use the new product restrictions data structure to restrict the products shown in the CMS. Depending on a plugin property, hide restricted products, or show them as POA, or better still extend the POA idea (webcatalog), so that restricted products can have different text to POA. i.e "POA text" and "Restricted Text" as two seperate properties of the plugin.