Cleaned up print/logging

[LonnekeScheffer]

I found it annoying that the regular immuneML print statements are not shown in the log file. I think much of the logging becomes more understandable by knowing where during the immuneML run it was encountered.

Added print_log utility function:

• to be called instead of print
• prints with flush AND writes to logging.info
• takes care of optional datetime in front of print statement

Fix in log function: logging of entering/exiting methods showed datetime double (because it was added inside log() as well as logging.basicConfig.format)

Some examples of log files using the old code vs this new code: old_logfile_example.txt new_logfile_example.txt

[LonnekeScheffer]

small fixes added later:

• correctly change the y axis title in FeatureDistribution plot
• correct failing test on github due to insignificant errors in renyi entropy values