edl: fix offset of user-visible chapters

Basically, chapter marks and chapter seek-points were incorrect, while
the rest worked.
edl: extend with chapter timestamps

Example see edl-mpv.rst.

What is this useful for? No clue...
player: fix start time if timeline is used (ordered chapters, EDL)

When timeline was used, and the --start option was not used, the initial
seek (needed to switch to the first timeline segment) seeked to -1 due
to an oversight.
command: export codec for each track
command: export list of editions as properties