Differential cached import mechanism and other refactorings

These commits are related to the implementation of a system that caches imported CSV files and compare new files with cached ones, in order to work with differences and obtain a huge boost on repetitive tasks.

Other refactorings regarding management tasks using the new ETL api have been done.

The docker-compose.yml file now uses the container_name directive, so that the docker machine in the gitlab runner can use the latest docker-compose image.