display yt-dlp version, multiple downloads enabled.

code refactoring
preparations for optimistic ui updates for new downloads

frontend/src/atoms/ui.ts

@@ -1,6 +1,12 @@
 import { atom } from 'recoil'
+import { RPCResult } from '../types'
 
 export const loadingAtom = atom({
   key: 'loadingAtom',
   default: true
+})
+
+export const optimisticDownloadsState = atom<RPCResult[]>({
+  key: 'optimisticDownloadsState',
+  default: []
 })