Uses dumb-init to improve PID 1 processing.
Uses dumb-init to improve PID 1 processing.

 - Split into 2 layers so that common apt-get are in one layer
   which can make pulling faster and rebuilding faster.
 - Use dumb-init instead of shell to handle PID 1 better.

raycoll/docker-plex-media-server,wernight/docker-plex-media-server