Register for push notifications

This sets it up so the homeserver will give us push notifications, but
we aren't handling them yet.

src/controller.h

@@ -11,6 +11,7 @@
 #include <Quotient/accountregistry.h>
 #include <Quotient/jobs/basejob.h>
 #include <Quotient/settings.h>
+#include <qcorotask.h>
 
 class NeoChatRoom;
 class TrayIcon;
@@ -124,6 +125,10 @@ public:
 private:
     explicit Controller(QObject *parent = nullptr);
 
+    // note: this is intentionally a copied QString because
+    // the reference could be destroyed before the task is finished
+    QCoro::Task<void> setupPushNotifications(QString endpoint);
+
     QPointer<NeoChatConnection> m_connection;
     TrayIcon *m_trayIcon = nullptr;