function `setTxOnly` missed in pynorm/session.py

[honglei]

As topic

    def setTxOnly(self, txOnly:bool=False, connectToSessionAddress:bool=False):
        '''
            void NormSetTxOnly(NormSessionHandle sessionHandle,
                       bool              txOnly,
                       bool              connectToSessionAddress)
        '''
        libnorm.NormSetTxOnly(self, txOnly, connectToSessionAddress)