Backup - Restore

Hi @caelys! There is an old pull request regarding backup and restore, but it pre-dates the great big tutor v3 refactoring: https://github.com/regisb/tutor/pull/107
I want to add tutor local backup and tutor local restore commands; meanwhile, what you can do is simply to backup the project root located at $(tutor local printroot): all the data and configuration is located in this folder.