Add Travis CI setup to project

[andmor-]

This PR adds Travis CI support to the project. The only modified file from the master branch is package-lock.json, the rest are additions which do not interfere with the previous code. The project is built on Docker by the build-with-docker.sh script in order to normalize the build across different platforms. The build-with-docker.sh script is automatically called by Travis CI on every push in order to verify CI. When a tag is created, Travis CI will automatically create a tarball containing the build output and deploy this tarball on the corresponding GitHub release entry. The Docker build triggered by the build-with-docker.sh script, uses build.sh to run the actual code build inside the docker image. The build.sh script can also be used locally to build the image outside docker. This will most likely cause changes on package-lock.json for every different environment where it is built (unless the "ci" parameter is passed: build.sh ci and the available npm version is >6.1), so after this PR is merged, the package-lock.json file should not be committed anymore, unless it is recreated inside the Docker image (via build-with-docker.sh). The Dockerfile extends a CLARIN image created specifically to provide the necessary environment to build the LRSwitchboard. This image is nothing more than an Alpine linux image with webpack and npm installed on it and is hosted here: https://gitlab.com/CLARIN-ERIC/docker-alpine-clrs-build_env

[claus-zinn]

I've merge the pull request with the base branch