View assets detail and download operation (#198)

* Fixed not displaying default user profile picture

* Added buttons to close viewer and micro-interaction for navigating assets left, right

* Add additional buttons to the control bar

* Display EXIF info

* Added map to detail info

* Handle user input keyboard

* Fixed incorrect file name when downloading multiple files

* Implemented download panel

web/src/lib/stores/download.ts

@@ -0,0 +1,13 @@
+import { writable, derived } from 'svelte/store';
+
+export const downloadAssets = writable<Record<string, number>>({});
+
+
+export const isDownloading = derived(downloadAssets, ($downloadAssets) => {
+  if (Object.keys($downloadAssets).length == 0) {
+    return false;
+  }
+
+  return true;
+})
+