autoplay next video support for playlists

client/src/app/shared/images/global-icon.component.scss

client/src/app/shared/users/user.model.ts

...-playlist/video-playlist-element-miniature.component.scss

...p/videos/+video-watch/video-watch-playlist.component.html

...p/videos/+video-watch/video-watch-playlist.component.scss

...app/videos/+video-watch/video-watch-playlist.component.ts

...nt/src/app/videos/+video-watch/video-watch.component.html

client/src/app/videos/+video-watch/video-watch.component.ts

client/src/app/videos/+video-watch/video-watch.module.ts

.../videos/recommendations/recommended-videos.component.html

...pp/videos/recommendations/recommended-videos.component.ts

server/controllers/api/users/me.ts

server/helpers/custom-validators/users.ts

server/initializers/constants.ts

...er/initializers/migrations/0460-user-playlist-autoplay.ts

server/models/account/user.ts

shared/models/users/user-update-me.model.ts

shared/models/users/user.model.ts