Reduce docker image size and simplify docker-compose setup

[jasonxh]

This PR is geared towards docker usability. The previous PR (#276) has already taken us a long way, by introducing Traefik to automate TLS setup. This PR addresses a few more pain points around docker and docker-compose.

• Reduce docker image size by roughly 50%, by not producing unnecessary intermediate layers.
• Update docker image base to node:8-alpine.
• Simplify docker-compose.yml by removing unnecessary configs.
• Consolidate all must have customization in .env file. Get rid of config duplication for domain name.
• Remove the implicit assumption on external docker networks.
• Standardize on docker volumes for state persistence.
• Move docker-compose setup back to deployment/docker-compose, to be consistent with the other two deployment modes.
• Add package-lock.json for version locking.

NOTE
Users of the updated docker-compose.yml will have to build their own images for now, until the official image openhab/openhabcloud-app is refreshed, due to some underlying changes (i.e. run-app.sh).

[marziman]

Thanks @jasonxh ,
I will test and review it.

[digitaldan]

I tested this a little and all seems to work, thanks!