WebUI: fix showing required asterisk '*'
    
    There was a bug that when user switch between two facets where is
    required field and in one of them is writable and in second one
    is not writable, then the asterisk which marks required field is
    not shown. i.e. admin vs. user details page or global_passwd_policy
    vs. other_passwd_policy details page.
    
    That was caused by incorrect evaluation of required state of field.
    Evaluation works that way: evaluate old required state, then evaluate
    current required state and if states has changed then emit change event.
    The evaluation depends on writable and read_only state of field.
    Those two states are set before evaluation of required state, but
    their old values (for evaluating previous required stated) were
    not stored anywhere.
    
    This commit adds two attributes which stores old writable
    and read_only states. The required asterisk is then shown correctly.
    
    https://pagure.io/freeipa/issue/6849
    
    Reviewed-By: Petr Vobornik <pvoborni@redhat.com>