Fixed incorrect raising of PaperError

Added calendar initialisation via configuration

Renamed week() to make_week()

Major revamp of configuration handling ...

• Moved configuration file loading into Configuration class.
• Added config getter methods to Configuration.
• Updated and extended custom exception types.
• Restructured error handling.
• Factored out app name.

Fixed broken “offsets” for INFO202/S2

Deleted obsolete comment

Converted load_config() into Configuration class

Removed reference to PROG constant

Moved load_config() into config.py

Added configuration defaults ...

The app nows looks for configuration in ~/.config if no configuration
file is explicitly specified. If the default configuration isn’t found,
a default configuration file is copied into ~/.config.

Refactored program name

Renamed module