First run at a folder blocktype, required for the template migration.
Displays a folder and its contents. Sadly, the artefact chooser doesn't make it very easy to sort the results in a 'folder and its children' type way. Also sadly, files added to folders will not be available in the view for up to a minute, until the artefact parent cache is rebuilt. This problem is fixable later in the same way that it was for the resume field stuff, but the work isn't worth it right now.