webui: send API version in RPC requests
    
    Currently there is an incorrect behavior that server doesn't send datetime
    and dnsname data in new format.
    
    This patch adds the version to each RPC request making the UI look as  the
    latest client. Server then sends data in correct format. It also removes
    the "unknown version" warning from each RPC response.
    
    https://fedorahosted.org/freeipa/ticket/4394
    
    Reviewed-By: Endi Sukma Dewata <edewata@redhat.com>