Add support to run development/build in a docker container

[NevarrTivianne]

Apologies for not doing a PR but you might want to switch things around.

# cat docker/Dockerfile
FROM openjdk:11.0.8-slim-buster

RUN apt-get update && \                                                         
    apt-get install -y nodejs npm && \                                          
    npm install -g yarn                                                         
WORKDIR /data

# cd docker && docker built -t everoute11 .

Running it:

docker run -it -v "${PWD}:/data" -p "8080:8080" -rm everoute11 bash

Inside both frontend and backend building works.

One major downside: gradle will install itself into /root/.gradle (550 MB here) and you lose that progress.

I solved that with another mkdir .gradle-home && ln -s /data/.gradle-home /root/.gradle in the container's bash, but this should be done in the Dockerfile. Then add .gradle-home to .gitignore

Also connecting to mongo:27017 instead of localhost.