Let the `converse-loaded` event conform to the CustomEvent spec

https://developer.mozilla.org/en-US/docs/Web/API/CustomEvent/CustomEvent

docs/source/configuration.rst

@@ -1670,6 +1670,7 @@ For example:
 
     initConverse(shadowRoot) {
         window.addEventListener("converse-loaded", function(event) {
+            const { converse } = event.detail;
             converse.initialize({
                 root: shadowRoot,
                 // Other settings go here...

src/components/message-history.js

@@ -121,7 +121,6 @@ export default class MessageHistory extends CustomElement {
     }
 
     renderMessage (model) {
-        // XXX: leaky abstraction "is_only_key" from converse-omemo
         if (model.get('dangling_retraction') || model.get('is_only_key')) {
             return '';
         }

src/headless/converse-chat.js

@@ -578,11 +578,8 @@ converse.plugins.add('converse-chat', {
             },
 
             updateMessage (message, attrs) {
-                // Overridden in converse-muc and converse-mam
                 const new_attrs = this.getUpdatedMessageAttributes(message, attrs);
-                if (attrs) {
-                    message.save(new_attrs);
-                }
+                new_attrs && message.save(new_attrs);
             },
 
             /**

src/headless/converse-core.js

@@ -1655,6 +1655,5 @@ Object.assign(converse, {
  * @event converse-loaded
  * @example window.addEventListener('converse-loaded', () => converse.initialize());
  */
-const ev = new CustomEvent('converse-loaded')
-ev.converse = converse;
+const ev = new CustomEvent('converse-loaded', {'detail': { converse }});
 window.dispatchEvent(ev);

src/headless/converse-muc.js

@@ -1795,7 +1795,6 @@ converse.plugins.add('converse-muc', {
 
 
             getUpdatedMessageAttributes (message, attrs) {
-                // Overridden in converse-muc and converse-mam
                 const new_attrs = _converse.ChatBox.prototype.getUpdatedMessageAttributes.call(this, message, attrs);
                 if (this.isOwnMessage(attrs)) {
                     const stanza_id_keys = Object.keys(attrs).filter(k => k.startsWith('stanza_id'));