add docker installation

[nilsnolde]

docker-compose build pgrserver
docker-compose up -d

No need for Java and maven, but the topology still needs to be manually created before. Also sets up the PostGIS container if desired.

For easier deployment I switched the application.properties Postgres variables to use env vars with defaults, so nothing breaks compared to master.

Sorry for the README diffs, Atom introduced them when saving..

[nilsnolde]

minor change: maybe include mvn dependency:resolve in the dockerfile so deps are downloaded inside the image, not for every container?

[mbasa]

I merged this with develop and will push into master after a few testing. Thank you very much for this.