WebUI: add method for disabling item in user dropdown menu
    
    AD user can do only several things. One of those which are not
    allowed is to reset password to itself. Therefore we need to be
    able to turn of a item in dropdown menu. In our case
    'Password reset' item. Function which disable menu item and detach
    the listener on click from the item specified by its name was added.
    
    Part of: https://pagure.io/freeipa/issue/3242
    
    Reviewed-By: Petr Vobornik <pvoborni@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>