Adapt hillas calculation script to MAGIC reader v0.2.0

This merge request implements #8 (closed). hillas_preprocessing.py still uses different event source classes for real and simulated MAGIC data, as it was in the MAGIC reader v0.1.0. Now ctapipe_io_magic is updated to v0.2.0, where only one common event source class, MAGICEventSource, is used to read MAGIC data. Therefore hillas_preprocessing.py should be updated to follow the change in the MAGIC reader.