Do not display the + for folders empty of sub-folders

At the moment when you create a folder and add a file into it you will see a small triangle which mean "this folder is full of something". It's sending a mixed messaged since it's in the folder tree view you think you can unfold to see a new folder.

We need to change this behaviour for the message to mean "There are sub-folders in here".

We won't check for files into folder but only for sub-folders.