WebUI: Add support for suppressing warnings
    
    Each command can have specified an array of warning codes which will
    be suppressed and won't be shown.
    
    For specifying this it is necessary to set command property
    'supressed_warnings: [codes_of_warning]'
    
    Part of: https://pagure.io/freeipa/issue/6618
    
    Reviewed-By: Petr Vobornik <pvoborni@redhat.com>