Allow skins to override js and css from base skin that are inside a folder on filesystem

Currently, Wiki Skins are able to override a css/js file that is inside a folder on filesystem using .(dot). Example.
mycssfiles/mycssfile.css that is loaded using jsfx.use can be overriden by attaching to the skin an attachment with name mycssfiles.mycssfile.css. Since properties allow .(dot) to be used in their names, i propose we make skins able to override filesystem files using the same name as with the attachment name.