Add post-login complete security flow

This adds a step after login to complete security for your new session. At the
moment, the only verification method is entering your SSSS passphrase, but nicer
paths will be added soon.

This new step only appears when crypto is available and the account has
cross-signing enabled in SSSS.

Fixes https://github.com/vector-im/riot-web/issues/11214

src/settings/Settings.js

@@ -1,7 +1,7 @@
 /*
 Copyright 2017 Travis Ralston
 Copyright 2018, 2019 New Vector Ltd.
-Copyright 2019 The Matrix.org Foundation C.I.C.
+Copyright 2019, 2020 The Matrix.org Foundation C.I.C.
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -153,7 +153,6 @@ export const SETTINGS = {
         displayName: _td("Enable cross-signing to verify per-user instead of per-device (in development)"),
         supportedLevels: LEVELS_FEATURE,
         default: false,
-        controller: new ReloadOnChangeController(),
     },
     "feature_event_indexing": {
         isFeature: true,