Add CI/CD

[ricardobalk]

Now we have Dockerfiles (#25), it would be cool if the project has some kind of CI/CD, like Travis, Jenkins, GitHub Actions, etc.

Docker provides an environment and a default setup for the application, CI/CD can take advantage of that.

Main goals for CI/CD

• Runs common linters and formatting tools on source tools (e.g. go fmt, go vet, npx prettier)
  — and commit automatically fixed lines to the PR
• Checks the resulting PR for compatibility (i.e. failed Docker builds should not pass)

Bonus points for

• If the CI/CD checks availability of the API endpoint (i.e. does the API really work?)
• If the CI/CD checks availability of the map interface by making screenshots with something like Puppeteer
  — but this stuff probably involves complex stuff like xvfb, as most CI/CD systems are headless and don't have a "real display".

[ricardobalk]

Basic CI/CD has been created now. Travis CI installs Docker, docker-compose, sets up environment variables and runs docker-compose build. This builds the front-end and the back-end. If anything fails, Travis CI will also fail, and you'll see a red cross ❌.

Next thing for me to create is to let Travis run linters against the code in the repository, before building them.

[ricardobalk]

Need to add CI/CD again in favour of #56