clear bitmaps on file reload

src/components/Picker.vue

@@ -42,6 +42,7 @@ export default class Picker extends Vue {
           });
 
         Promise.all(bitmapPromises).then((bitmaps) => {
+            this.bitmaps = {};
             bitmaps.forEach(([filename, bitmap]) => {
                 this.bitmaps[filename] = bitmap;
             });