[Docker] Move from signalk user to node user
[Docker] Move from signalk user to node user

There isn't a real good reason to have a separate signalk user inside
the container. This commit removes the need for a signalk user and
moves the app to /home/node/signalk.

SignalK/signalk-server-node,SignalK/signalk-server-node,SignalK/signalk-server-node,SignalK/signalk-server-node