EEG Docker - Stable first public version (release candidate 1)

This project creates a Ubuntu docker image and pushes it to docker.com.
The image is based on rocker/r-ubuntu:18.04 (see https://hub.docker.com/r/rocker/r-ubuntu) and has Ubuntu 18.04 LTS. In addition, several apt and r packages are pre-installed so to run continuous integration on EEG projects via CircleCI.