#51: Add websocket endpoint for widget events

[nikochiko]

Closes #51 along with #59

Changes:

• Added ws endpoint at ws://domain/ws/widgets/<user_id>
• Accepts events as json-data:
  • A ws message with text {"event": "click"} would increment clicks and {"event": "impression"} would increment impressions

Preferred way to run in production is using daphne: daphne -p 8000 hyperlog.asgi:application