rework tom's welcome page to fit in slightly better with riot's UI/UX

* moves login button to top-left
* switches from iframe to a request() to load the welcome page to inherit CSS (probably breaks RTS :/)
* namespace CSS
* change the layout a bit.

src/skins/vector/css/matrix-react-sdk/structures/_LoginBox.scss

@@ -0,0 +1,36 @@
+/*
+Copyright 2017 OpenMarket Ltd
+
+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.
+*/
+
+.mx_LoginBox_loginButton_wrapper {
+    text-align: center;
+    width: 100%;
+}
+
+.mx_LoginBox_loginButton {
+    margin-top: -8px;
+    height: 40px;
+    border: 0px;
+    border-radius: 40px;
+    padding-left: 1em;
+    padding-right: 1em;
+
+    background-color: $accent-color;
+    color: $primary-bg-color;
+
+    cursor: pointer;
+
+    font-size: 15px;
+}