Restricting customers to use certain packages.

This update allows a customer to be directed to use certain packages.

Previously, All packages were available to all.  Packages were checked in order until one that passed was found.

There is a proviso that a package can contain a restriction allowing only certain customer to use that package.

The problem with this approach is that is does not stop a customer from using an inappropriate package if that package is in the list first.

This update adds a list of permitted packages which is in the customer pricelists screen. 

When a package is being checked then it is checked against the list of packages allocated to that customer.  Only if it is in that list (or no packages are allocated to the customer - the default) then the package is processed further. The default is to allow all packages to be available for the customer.

So,  if a package is only available to a certain customer(s) then in the package, the customer(s) should be recorded in the package details and the package added in the customer record.