Grand-challenge-forge

- Various improvements to spelling and comments in the challenge packs

- Fixed passing `'is_image'`, `'is_json'` to the prediction.json example of the evaluation method
- Added a generic `read_file()` / `write_file()` to the evaluation.py and inference.py of the algorithm and evaluation examples, respectively

- Adds challenge packs, consisting of:
- example upload algorithm
- example submission algorithm
- example evaluation method