PACSSeries registration over celery task and WebSockets for streaming DICOM receive progress messages

[jennydaman]

• Replaced gunicorn with daphne. We are now using ASGI instead of WSGI.
• Added a WebSockets endpoint where clients can listen to DICOM receive progress notifications. The WebSockets endpoint is authenticated with a ?token=xxxx query string.
• Removed POST request for registering PACSSeries. It is now instead a celery task.