Library does not check access permissions of files and folders

[dschreij]

See #10 (comment) for a more elaborate discussion. The problem lies largely with the OSF API though, as it doesn't show access permissions for the user per file/folder node, but only at the level of the project nodes. The QOSF library thus has to propagate this access information to all the project's underlying file and folder nodes, which appears very error prone to me (assumption is the mother of all ...)