Enhance store.py (save_detections) for fall detection

[ivelin]

Is your feature request related to a problem? Please describe.
Currently save_detections expects a bounding box for detections. This is the case for object detection and face detection, but not for pose detection and fall detection.

Describe the solution you'd like
Enhance detection event schema for storage, notifications and UI display.

Describe alternatives you've considered
Currently fall_detection is forced to output a fake bounding box to fit the expected format, but that's not optimal.