SMI safety monitoring interface

[gruenst]

Just a comment, as this hasn't been reported yet:
the library not only works for Solaredge inverters, but also for the SMI (Safety and Monitoring Interface). So optimizer data of systems with other inverter units could be logged.

Quick startup guide:

1. connect to the RS232 interface of the SMI with serial number 12345678 (e.g. via USB to RS232 adapter) in order to retrieve the private key of the SMI:
   python semonitor.py -c 12,H239/12,H23a/12,H23b/12,H23c -s 12345678 -t 2 /dev/ttyUSB0|python utilities/sekey.py -o 12345678.key
2. dump the daily data as described in the library (e.g. via RasPi with IP 192.168.x.x between SMI and router):
   sudo tcpdump -i any -w dump_file.pcap -s 0 tcp and src 192.168.x.x and greater 50
3. decrypt daily data with retrieved key (1) and output to json file:
   python semonitor.py -k 12345678.key -o output.json dump_file.pcap

Thanks everyone for contributing to this library!