Use EventTarget

Getting torrent info from servers now uses Events
instead of magic callbacks.

js/trserver.js

@@ -1,6 +1,6 @@
 "use strict";
 
-class trserver {
+class trserver extends EventTarget {
     #rpcurl;
     #authHeader;
     #sessionHeader;
@@ -9,9 +9,18 @@ class trserver {
     #isOnline = false;
 
     #logger = function(msg) {};
-    #torrentCallback = function(hash, torrentInfo) {};
+    #torrentCallback = function(hash, torrentInfo) {
+        let e = new CustomEvent('torrent-update', {
+            'detail': {
+                'torrentHash': hash,
+                'torrentInfo': torrentInfo
+            }
+        });
+        this.dispatchEvent(e);
+    };
 
-    constructor (initdata, logger, tcb) {
+    constructor (initdata, logger = null, tcb = null) {
+        super();
         this.#rpcurl = initdata.rpcurl;
         if (logger != null) {
             this.#logger = logger;