Clear more state in DeviceListener

Especially the devices at start, otherwise they'll just be wrong
if you log in after logging out.

src/DeviceListener.js

@@ -78,6 +78,8 @@ export default class DeviceListener {
         this._dismissedThisDeviceToast = false;
         this._keyBackupInfo = null;
         this._keyBackupFetchedAt = null;
+        this._ourDeviceIdsAtStart = null;
+        this._displayingToastsForDeviceIds = new Set();
     }
 
     /**