Feature: ask what services are out of date

[lagartoverde]

We want to expand the functionality of this tool and add a command to check what docker images of the docker-compose.yml file are out of date.

This command would read all the docker images from the current project and make requests to the docker-hub api in order to check what's the most recent version of that image.

After that it would print a line for each outdated image specifying the actual installed version and the latest version on docker-hub