Added ConfigManager to preserve some values. Fixes #221

Actually, PermissionError (and other errors like FileNotFoundError etc) are sub-classes of OSError. From Python3.3, OSError and IOError are the same - according to http://parenchym.com/pymblog/new-exception-hierarchy-in-python-33.html . With Python 2 it gave me always only IOError. So from my point of view it IS sufficient. However to prevent any potential problems I can just chenge it to "except (IOError, OSError) as e".