Tiled Importer "Collection of Images" Tileset support

[spinningD20]

Hi all, I wanted to put in a request to support what Tiled calls the type of tileset "Collection of Images", which is where you createa a tileset out of multiple png's, all of which may be arbitrarily sized. Right now, Luxe attempts to load this type of tileset and errors because it's looking for the source attribute on the wrong xml / json item.