Support different output formats (new export-scenes command)

[Breakthrough]

To ease the transition to supporting #156 and #323, the next version should include a new export-scenes command that will support multiple output formats. Ideally the command should be allowed to be specified twice, and allow some different output formats, e.g.:

scenedetect -i video.mp4 export-scenes --format=csv

scenedetect -i video.mp4 export-scenes --format=edl

scenedetect -i video.mp4 export-scenes --format=fcp

scenedetect -i video.mp4 export-scenes --format=qp

Open tracking bugs:

• FCP - Final Cut Pro X - XML File #156
• Chapter Formats - [Feature Request] Export scenes in chapter/XML format #323
• QP - QP file output #388

References:

EDL reference: https://github.com/mpv-player/mpv/blob/master/DOCS/edl-mpv.rst
Chapter formats: https://github.com/rigaya/NVEnc/blob/master/NVEncC_Options.en.md#--chapter-string
https://gist.github.com/schtritoff/8e0105060cb07c118863867429473830
Mtillmann/chaptertool#1