Minor examples fixes

[JesusMtnez]

This PR make minor fixes in examples so the work properly. It also updates documentation.

• todolist-lib:

  • Update README.md
  • Fix foreign key in todo_lists table
  • Fix drop methods in repositories

• todolist-http-finch:

  • Update README.md
  • Move TodoListApp to main package
  • Move APIs to http package
  • Remove unused implicit
  • Sort imports
  • Support env vars in application.conf

• todolist-http-http4s:

  • Update README.md

• In main README.md, all examples references have been updated