feat(web) add scrollbar with timeline information (#658)

- Implement a scrollbar with a timeline similar to Google Photos
- The scrollbar can also be dragged

web/src/lib/stores/album-asset-selection.store.ts

@@ -0,0 +1,10 @@
+import { writable } from 'svelte/store';
+
+function createAlbumAssetSelectionStore() {
+	const isAlbumAssetSelectionOpen = writable<boolean>(false);
+	return {
+		isAlbumAssetSelectionOpen
+	};
+}
+
+export const albumAssetSelectionStore = createAlbumAssetSelectionStore();