Dockerize + handle docker image

[michalmikolajczyk]

Is your feature request related to a problem? Please describe.
We need the project to run in a Docker container, so that hosting is easily manageble

Describe the solution you'd like
Please

1. add a Dockerfile,
2. make sure that the docker image is built on Travis CI builds

Describe alternatives you've considered
We thought initially about relying just on package-lock.json, but we cannot deploy node.js apps with the same ease as Docker images

Additional context
The blockchain node used by the dapp should be external, provided via env variables.