public function filter($category_id)
 {
     $gallerySeries = GallerySerie::where('category_id', '=', $category_id)->orderBy('position')->get();
     $galleryCategories = GalleryCategory::lists('name', 'id');
     return view('gallery-series.index', compact('gallerySeries', 'galleryCategories', 'category_id'));
 }