Fix docker

Fixes #7 (closed)

• Updates node version for front-end image
• Adds docker ignore file to avoid copying unnecessary files in the containers
• Moves run_server.sh script to project root so that it can be used to process datasets outside docker containers as well
• Updates backend image so that it reuses existing container and does not do processing if a dataset is not specified
• Moves cartolab.db, bitmaps and static directories under generated directory in the project root
• Uses docker volumes so that consecutive container runs can use already processed data
• Update README.md for docker usage instructions