add Docker files

First step in building the docker images for this project:

• Add Dockerfile
• Add docker-compose.yml to clarify how it should be used
• Add assertion to import of json as otherwise did not build for me
• Move start npm script to forever
• start script now does not use forever

Next steps:

• Build docker image with gitlab-ci

• Define if we want different stages for this as well or if one universal deployment is sufficient
  Currently all versions use the same website but I propose to have

  • dev.push.recoverycat.de for development builds
  • push.recoverycat.de for production builds

  We still need to figure out how to make the code use the different servers though.

• Deploy with gitlab ci