No more xml differentiation for 'scratch' type of comments.

src/engine/comment.js

@@ -26,7 +26,7 @@ class Comment {
     }
 
     toXML () {
-        return `<comment type="scratch" id="${this.id}" x="${this.x}" y="${
+        return `<comment id="${this.id}" x="${this.x}" y="${
             this.y}" w="${this.width}" h="${this.height}" pinned="${
             this.blockId !== null}" minimized="${this.minimized}">${this.text}</comment>`;
     }