Fix an issue that folder.create_folder creates root directory

When calling

```ruby
root_folder = storage.root.folders.find {|folder| folder.name == 'my_folder'}
root_folder.create_folder('my_sub_folder')
```

creates 'my_sub_folder' in the root directory.
This commit fixes the issue.
small refactor
todo, refactor to remove rspec warning
add a todo file
version bump