Output gets messed up on the message pane

[johann-petrak]

Output from the user function and the gatenlp interaction lib gets mixed up in a strange way on the message pane. This is probably caused by both ultimately getting copied to stdout on the java side, but coming from two different pipes.
Need to check how to properly flush stdin/stderr as well as the logger on the python side to make this work.

[johann-petrak]

This has been fixed by changing gatelib-interaction: instead of copying the streams using byte buffers, we copy line by line and flush each line. That way, if several streams get copied to the same output stream in parallel threads, it should be less likely for things to get mixed up.