Implement Docker image building and publishing for deployment

[maltezacharias]

Switch deployment process to publishing of ready-built docker containers to e.g. DockerHub or a private registry.

• Create build scripts to create and push new containers
• Implement automatic image building and pushing process using a suitable mechanism (Travis? DockerHub automated builds?)
• Investigate whether we should use docker image signing for this?
• Design a workflow where pushing to a designated protected branch on github will result in an automatic building and deployment of the branch

[Baschdl]

• docker exec backend python3 manage.py migrate and docker exec backend python3 manage.py check have to be executed on the server
• Ignore the database when building

[Baschdl]

Dockerhub repository: https://hub.docker.com/r/match4everyone/match4healthcare/tags
It's important to login on the terminal you try to push from