Extend table facet
    
    There is new attribute of table facet which allows to set which column of
    table will be its primary key. This patch also move some code into separate
    method - it will be easier to overide some functionality in child classes.
    
    Part of: https://fedorahosted.org/freeipa/ticket/5906
    
    Reviewed-By: Petr Vobornik <pvoborni@redhat.com>