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/artist_credit.sql

@@ -23,3 +23,6 @@ WHERE id = ?;
 -- name: DeleteArtistCredit :exec
 DELETE FROM artist_credit 
 WHERE id = ?;
+
+-- name: DeleteAllArtistCredits :exec
+DELETE FROM artist_credit;