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

backend/database/sql/queries/audio_files.sql

@@ -71,6 +71,9 @@ LEFT JOIN cover_art ca ON rg.cover_art_id = ca.id
 WHERE af.file_path = ?
 LIMIT 1;
 
+-- name: DeleteAllAudioFiles :exec
+DELETE FROM audio_files;
+
 -- name: GetAudioFilesByReleaseGroup :many
 SELECT
     af.file_path,