mtDNAcombine - 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 manicaeeg/eeg-docker (see https://hub.docker.com/r/manicaeeg/eeg-docker) and has Ubuntu 18.04 LTS. In addition, several apt and r packages are pre-installed so to run continuous integration on the EEG mtDNAcombine project via CircleCI. The docker is pubicly available at: https://hub.docker.com/r/manicaeeg/eeg-mt-dna-combine