Dragndrop preview film tiles

- import go jquery-ui
- Basic implementation without styling
- only swapping is possible (no insertion)

js/piskel.js

@@ -73,7 +73,7 @@ $.namespace("pskl");
 
       this.previewsController = new pskl.controller.PreviewFilmController(
         frameSheet,
-        $('#preview-list')[0], 
+        $('#preview-list'), 
         previewTileCanvasDpi
       );