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/async-components/views/dialogs/secretstorage/CreateSecretStorageDialog.js

@@ -313,7 +313,7 @@ export default class CreateSecretStorageDialog extends React.PureComponent {
             <p>{_t(
                 "Secret Storage will be set up using your existing key backup details. " +
                 "Your secret storage passphrase and recovery key will be the same as " +
-                " they were for your key backup",
+                "they were for your key backup.",
             )}</p>
             <DialogButtons primaryButton={_t('Next')}
                 onPrimaryButtonClick={this._onMigrateNextClick}