[wip][br3] edit screen

[shish]

Assumes an API:

• GET /api/edit/:trackId - get a list of which source variants exist

{
    "subtitles": ["Default"],
	"media": {
		"Vocal": ["mp4"],
		"Instrumental": ["webp", "ogg"]
	},
}

• GET /api/edit/:trackId/tags - get a list of the exact tags in the .txt file (tracks.json doesn't map 1:1 with the .txt file because some tags are added (eg we dynamically add an aspect_ratio tag based on the source media) and some are removed (eg moderator notes))

{
	"title": ["My Track"],
	"from": ["TV Show"],
	"artist": ["Alice", "Bob"]
}

• POST /api/edit/:trackId/tags - takes the same tags dictionary as above as input, writes it to a .txt file, with an updated:YYYY-MM-DD tag added
• GET /api/edit/:trackId/subs/:variant - get subtitle data in JSON-sub format

[
	{
		start: 123.4,
		end: 567.8,
		top: false,
		text: "The first line of the song"
	},
	...
]

• POST /api/edit/:trackId/subs/:variant - accepts subtitle data in JSON-sub format and writes .srt to disk
• POST /api/edit/:trackId/rename_subs - renames a subtitle variant

{
	"from": "Default",
	"to": "Romaji"
}