Fix some miscellaneous weirdness around push notifications

For some reason, I *stopped* the timer if we get a push message - which
makes *no* sense. It meant that NeoChat kept running in the background
for basically no reason.

We can also make the NotificationsManager::postPushNotification function
static and avoid creating some singletons.

src/app/notificationsmanager.cpp

@@ -388,7 +388,7 @@ void NotificationsManager::postPushNotification(const QByteArray &message)
 
 #ifdef HAVE_KIO
         auto openAction = notification->addAction(i18n("Open NeoChat"));
-        connect(openAction, &KNotificationAction::activated, this, [=]() {
+        connect(openAction, &KNotificationAction::activated, notification, [=]() {
             QString properId = roomId;
             properId = properId.replace(u"#"_s, QString());
             properId = properId.replace(u"!"_s, QString());
@@ -402,8 +402,6 @@ void NotificationsManager::postPushNotification(const QByteArray &message)
         connect(notification, &KNotification::closed, qGuiApp, &QGuiApplication::quit);
 
         notification->sendEvent();
-
-        m_notifications.insert(roomId, {json["ts"_L1].toVariant().toLongLong(), notification});
     } else {
         qWarning() << "Skipping unsupported push notification" << type;
     }