- Cleanup

- Improved exception on connection error
- command port is now opened between scenes

* fix for name change: from USER_PREFERENCES to PREFERENCES

* Introduced retries on connecting

* Modified tests, sending 50 commands now, one after another, as a stress test
* Added a shutdown of connection before closing [link](https://docs.python.org/2/library/socket.html#socket.socket.close)
* Added a 1s. timeout

Merge remote-tracking branch 'origin/master'

Updated for Blender 2.80

Working blender command port