Live Thumbnails on seekbar

[tjenkinson]

• https://github.com/tjenkinson/hls-live-thumbnails for backend
• clappr plugin needs updating to understand thumbnails manifest

[tjenkinson]

https://github.com/LA1TV/Website/tree/feat-live-thumbnails

[tjenkinson]

#894

[tjenkinson]

Still need to do front end and support media item streams.