Add JsonFileRoomStorage and JsonFileTrackingStorage implementations
that implement the RoomStorage and TrackingStorage ports.
- Stores room data at ~/.jigaido/data/<room_id>.json
- Stores tracking data at ~/.jigaido/tracking/<room_id>_<user_id>.json
- Implements all port methods: load, save, add_bounty, update_bounty,
delete_bounty, get_bounty for rooms; load, save, track_bounty,
untrack_bounty for tracking
Fixes#9
