Reduce verbosity by replacing `print` calls by logging with different levels

Originally from the Orekit forum: https://forum.orekit.org/t/removing-jvm-already-started-message/3873

• Replace print("JVM already started, resuming on started JVM") in orekit_jpype.py by calling Python's logging method with logging.DEBUG level
• Also replace the print calls in pyhelpers.py by logging calls with logging.WARNING or logging.ERROR level depending on the case
  • Even better, throw exceptions when no orekit data source is found

https://docs.python.org/3/library/logging.html#logging-levels