Use official TMS docker images instead of personal repositories

Merged Máté Cserép requested to merge 116-official-docker-images into develop
  • Update config.params.php to use official images.
  • Update .gitlab-ci.yml to use official images.
  • Update existing tasks in the DB to avoid redundancy in the used images. Note, that currently the automated tester does not download images upon testing, since they are downloaded during the configuration by the instructor.

Closes #116 (closed)

Edited by Máté Cserép