New `track_list.json` format

[calaldees]

processmedia2 will have a new final step export_media.py to output a static file in the following format.

The track_list.json format will be changed to something like the following.

{
    'BASE62_HASH-TRACKID-11-characters': {
        'source_filename': '',  # For debugging
        'attachments': [
            {
                'url': 'PATH/BASE62_HASH.mp4',
                'use': 'preview',
                'mime': 'video/mp4',
            },
            ## if you want consistent image order then sort by url-string to get consistent order
        ],
        'duration': 300.0,
        'srt': 'SRT_TEXT',
        'tags': 'TAG_TEXT',
    }
}

I don't want multiple stages of transforms. I want as few data transforms as possible.

• It is up to the client to parse the SRT.
• It is up to the client to parse the tags.txt.
  • javascript will be provided for translating tag.txt into parent/child(s) - this is reasonably trivial.
  • This links/fixes to #21

[shish]

tracks.json has a fairly settled format now (see the code for the exact format, it's not exactly what was written here)