Hide products from groups of customers

It's written for B2BSuite and work on B2BSuite0.92

Currently there are two issues with this code:
1. The code works good with existing products but generates error when you create new product as it requires product_id which is not yet set for new product.
2. Once you set any product invisible for any groups - it becomes invisible for not logged in users forever. Even if you make it visible for all groups for not logged in users it still be invisible, you may make it visible for not logged-in user only through editing directly the database. Making visible/invisible for groups - there is no problems.

For detailed descriptions of issues please see todo.txt in archive.