Implement basic soft logout handling

Fixes https://github.com/vector-im/riot-web/issues/10235

CSS and copy are left as an exercise for a later iteration.

Login page handling is left for https://github.com/vector-im/riot-web/issues/10236

This implementation reuses as much of the Lifecycle flow as it can without causing problems. Most importantly, it requires https://github.com/matrix-org/matrix-js-sdk/pull/975 to be able to detect a soft logout and react to it. When it comes time to starting/stopping the Lifecycle, additional parameters are provided so that the auxiliary services can (re)start themselves without the client starting to sync.

src/components/views/dialogs/ConfirmWipeDeviceDialog.js

@@ -0,0 +1,60 @@
+/*
+Copyright 2019 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.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import React from 'react';
+import PropTypes from 'prop-types';
+import {_t} from "../../../languageHandler";
+import sdk from "../../../index";
+
+export default class ConfirmWipeDeviceDialog extends React.Component {
+    static propTypes = {
+        onFinished: PropTypes.func.isRequired,
+    };
+
+    _onConfirm = () => {
+        this.props.onFinished(true);
+    };
+
+    _onDecline = () => {
+        this.props.onFinished(false);
+    };
+
+    render() {
+        const BaseDialog = sdk.getComponent('views.dialogs.BaseDialog');
+        const DialogButtons = sdk.getComponent('views.elements.DialogButtons');
+
+        return (
+            <BaseDialog className='mx_ConfirmWipeDeviceDialog' hasCancel={true}
+                        onFinished={this.props.onFinished}
+                        title={_t("Clear all data on this device?")}>
+                <div className='mx_ConfirmWipeDeviceDialog_content'>
+                    <p>
+                        {_t(
+                            "Deleting all data from this device is permanent. Encrypted messages will be lost " +
+                            "unless their keys have been backed up.",
+                        )}
+                    </p>
+                </div>
+                <DialogButtons
+                    primaryButton={_t("Delete everything")}
+                    onPrimaryButtonClick={this._onConfirm}
+                    cancelButton={_t("Cancel")}
+                    onCancel={this._onDecline}
+                />
+            </BaseDialog>
+        );
+    }
+}