Allow number inventory move to unassigned extension

In the past when we deleted a user, the number would go back to unassigned extensions, now it goes to number inventory. It's more efficient, because all the numbers unassigned ext would forward to our main number. With Number inventory you have to manually assign each number to a temporary (dummy) extension and forward.

The old way IMO worked better with numbers going to unassigned ext after being removed from a user.