Consolidate all EventTile bubble stuff into its own component and use it for the room continuation plinth

src/components/views/messages/EventTileBubble.tsx

@@ -0,0 +1,34 @@
+/*
+Copyright 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.
+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, {ReactNode} from "react";
+import classNames from "classnames";
+
+interface IProps {
+    className: string;
+    title: string;
+    subtitle?: ReactNode;
+}
+
+const EventTileBubble: React.FC<IProps> = ({ className, title, subtitle, children }) => {
+    return <div className={classNames("mx_EventTileBubble", className)}>
+        <div className="mx_EventTileBubble_title">{ title }</div>
+        { subtitle && <div className="mx_EventTileBubble_subtitle">{ subtitle }</div> }
+        { children }
+    </div>;
+};
+
+export default EventTileBubble;