[Backport to 11.2] - [Regression] dashboard-wizard: date hierarchy reversed

Playing with the Dashboard Document Wizard demo on release/4.0, I stumbled across some odd behaviour that a date-based document ("Create a news document") produces a folder structure sorting by month first and by year afterwards. I'm attaching a screenshot of the result in the content perspective. I debugged this and concluded that this is a regression introduced into the plugin during the refactoring related to HIPPLUG-1470. The error is in the processing of the "notExistingFolders" list aroung line 490 of org.onehippo.forge.dashboard.documentwizard.NewDocumentWizardPlugin.

Please note that HIPPLUG-1470 suggests that the change is present not only on master and release/4.0 (12.0 maintenance), but has also been back-ported to CMS 11.2.