Add env_file normalization for each service : remove all duplicated env_file content

Change python shebang to python3

Fix docker-compose-normalize : the ports fields are not normalized anymore

Add normalize-docker-compose command which normalize the input docker-compose file by and converting all key-value string (e.g. 'foo=bar' or '80:8080') to key-value dicts inside the services' ports, labels and environment fields, and finally delete all duplicated volumes (and its preceding comments) for each services

Fix scalar type merge

• Fix merge and delete commands
• Add comment command

Handle None type merging

Add merge and delete commands