logging server

[franchuterivera]

Fixes printing ensemble selection messages to stdout by implementing a logging server.

[franchuterivera]

As discussed offline, py3.6 is a concern for the logging server (when n_jobs>1). We might look into dropping 3.6 support.

[mfeurer]

I didn't have a too close look yet, but this looks like it's very much going into the right direction. It appears that there are two things that require some more thought and/or work:

1. the error in Python3.6 right now happens because we pass a logger to the pynisher, which is then passed to a subprocess. The alternative would be to change the pynisher to accept a port and create the logger itself?
2. I guess the relevant changes need to be done for the evaluation, too?