- Implemented the logic around submission status (db-related and controller)
- Re-written the statuses for submission and file_submission
- Deleted submission-logic code from models.py
- Modified/implemented get submitted file status in controller
- Deleted PUT method on submission (from both views and controller) - it had no purpuse there, since the only data kept in a submission is a list of files, which can be either removed (DELETE) or added new ones (POST)