Add a dev server

• all local files (sources, dependencies, config, etc) are mounted in the devserver container
• devserver watch sources & rebuild/reload on each change
• "prod" server was updated to allow devserver to access its ressources
• "prod" server now use npm ci instead of install and webpack production mode for build

Closes #7 (closed)

.env.template

-# docker-compose components. Append ':devserver.yml' to also run the dev server (default is prod only)
+# docker-compose components replace by devserver.yml to run the dev server (default is prod) or append ':devserver.yml' to run both
 COMPOSE_FILE=docker-compose.yml
 # prod server host port
 PORT=8080