Added state and position update for Somfy shutters

[zapccu]

Hi,
this PR contains a lot of changes to your repo. I - more or less - rewrote somfy_shutter.py to support updates via mqtt for state and position of a shutter. The position is calculated by measuring the drive time (either manually or automatically).

To determine the up and down time of a shutter I introduced a new CALIBRATE command, which must be published in the payload of a mqtt set. I updated the doc in somfy.md accordingly. I also changed the config message sent to Homeassistant when the program is started (added state and position, removed optimistic).

I also made some minor changes to almost all other python files:

• Substituted some raise exception statements by logging statements to make the program more robust
• Added exception handlers for file I/O errors
• Handle signals to terminate the program gracefully when receiving a SIGTERM from systemd (prevent status "failed")
• Added a command line option for specifying an ini file
• Added a debug option to the ini file
• Added a logfile option to the ini file (all logging messages are written to this file)
• Fixed some bugs
• Added install.md with a description on how to install the program on a Debian or Raspbian system

Unfortunately there's still a bug in handling the Somfy device address. Actually the address must be stored in little endian format, currently it's in big endian format. So byte 1 and 3 should be swapped when composing the message. Changing this would break all existing device pairings. That's why I didn't change it.

Running the new version now for some days with 2 Somfy shutters and everything is working as expected.

BR