API breaking change: Fix broken playlist api

[Chocobozzz]

Breaking change of the undocumented playlist API (when listing videos, updating a playlist element or deleting an element from a playlist).

Unfortunately we made some mistakes when we designed these endpoints, and we have to change them:

• /api/v1/video-playlists/:playlistId/videos no longer accepts categoryOneOf, licenceOneOf, languageOneOf, tagsOneOf, tagsAllOf and filter query parameters.
• /api/v1/video-playlists/:playlistId/videos now returns { total: number, data: VideoPlaylistElement[] } // (before it was a Video object):

export enum VideoPlaylistElementType {
  REGULAR = 0,
  DELETED = 1,
  PRIVATE = 2,
  UNAVAILABLE = 3 // Blacklisted, blocked by the user/instance, NSFW...
}

export interface VideoPlaylistElement {
  id: number
  position: number
  startTimestamp: number
  stopTimestamp: number

  type: VideoPlaylistElementType

  video?: Video
}

• PUT and DELETE on /api/v1/video-playlists/:playlistId/videos/:videoId is now on /api/v1/video-playlists/:playlistId/videos/:playlistElementId

The goal of these changes is the API returns playlist elements even if they are unavailable or private.

Fixes #1867 & #1978