* trx_toolkit: do not auto power on/off child MS Transceivers
* trx_toolkit: use **kwargs in Transceiver.__init__()
* trx_toolkit: simplify Transceiver.power_event_handler()
* trx_toolkit/data_msg.py: legacy flag is only for version 0x00
* trx_toolkit/data_msg.py: introduce header coding version 0x01
* trx_toolkit/data_msg.py: implement header version coding