Improved handling of corsika.Library

Closes #718 (closed)

This update handles "unknown" directories by simply skipping them instead of throwing an error. For example,

In [2]: lib = corsika.Library("test_dir")
[WARNING] - corsika - Could not find a configuration file in test_dir/interaction_hist. Skipping sub-directory
[WARNING] - corsika - An error occured loading a RadioProcess: single positional indexer is out-of-bounds
[WARNING] - corsika - Unable to instantiate an instance of 'RadioProcess' for a process called 'CoREAS'. Skipping 'CoREAS'
[WARNING] - corsika - 'RadioProcess' object has no attribute '_RadioProcess__data'
[WARNING] - corsika - An error occured loading a RadioProcess: single positional indexer is out-of-bounds
[WARNING] - corsika - Unable to instantiate an instance of 'RadioProcess' for a process called 'ZHS'. Skipping 'ZHS'
[WARNING] - corsika - 'RadioProcess' object has no attribute '_RadioProcess__data'