The owncloud wizard already created the directory, but the recent addition
of FolderMan::checkPathValidityForNewFolder stopped allowing unexisting directories.
So change FolderMan::checkPathValidityForNewFolder to allow non existing directory
and whange the FolderWizard to create the directory if it does not exist.
Issue #3492
factorize the function to check the validity of a new folder out of
the folder wizard to the FolderMan.
There is even a test for it now.
That way we can also use it in the normal wizard
