Timestamps are unambiguous when using sub-sequences (e.g. 378 of 498
frames).  0-based sequential scene_idx was misleading.

- console top-N table: Scene column replaced with Timestamp
- CSV: scene_idx column removed, timestamp is the identity column
- parse_interframe_xml: drop scene_idx from returned dicts
Co-authored-by: Claude <claude@elphel.com>