add divider between tabs and regular buttons in room header

res/css/structures/_HeaderButtons.scss

@@ -0,0 +1,28 @@
+/*
+Copyright 2019 New Vector 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_HeaderButtons {
+    display: flex;
+}
+
+.mx_HeaderButtons::before {
+    content: "";
+    background-color: $header-divider-color;
+    margin: 2px 20px 5px 15px ;
+    border-radius: 2px;
+    width: 2px;
+}
+