improved library scan speeds, added library manager component

-libraries tab now opens a library manager
-choose library directory, manually soft scan and rescan
-batched db queues
-mp3 header-based duration extraction

frontend/src/events.ts

@@ -39,6 +39,7 @@ export const Events = {
     RequestRemoveTracksFromQueue: "RequestRemoveTracksFromQueue",
 
     // Library events
+    LibraryScanStarted: "LibraryScanStarted",
     LibraryScanComplete: "LibraryScanComplete",
 } as const;