Moved Importer class to c4dtools.importer

and get_root_module() with it.
Fixed exception in parse_and_prepare()
Enhanced Resource class implementation

- __getitem__() now returns a str, not a ResourceString
- Added type-safety for add_symbols()
- Added new_symbols() method
Renamed UserDataSetAndGet to UserDataManager

... and added type safety.
Adjusted for changes