Allow multiple unsetColumns calls

Grocery CRUD Enterprise
1

Hi @johnny!

I would love if you add support to allowing multiple unsetColumns calls without loosing all the previous ones, there are several use cases for this (like unsetting columns in a method or two).

        $crud->unsetColumns(['contactLastName']);
        $crud->unsetColumns(['phone']);
        $crud->unsetColumns(['city']);

Instead of

$crud->unsetColumns(['contactLastName', 'phone', 'city']);

Thanks in advance!