Improve logic of running command in PythonServer:

 - Make behavare more similar to interpreter - if we run single expression, print result of them to output
 - Remove code, which try to do the same thing (but don't work very well)
 - Move addition code for server working from session into server (init.py)
Also add setting worksheet path to python session (and forward passing the path to server, because Python use filename in traceback)