Add initialize item to import directory as nt:folder and nt:file hierarchy

It should be possible to import a directory of web resources into the repository with one initialize item.

For example, say we have the following files and directories in a packaged jar:

webresources/
css/
main.css
js/
script.js
hippoecm-extension.xml

It should then be possible to define an initialize item in the hippoecm-extension.xml file that points to the directory 'webresources'. The repository should then be able to bootstrap a hierarchy of nt:folder and nt:file nodes that reflects that directory and all directories and files below it (recursively).