Refactor messages model; New timeline react components

ts/components/conversation/LastSeenIndicator.tsx

@@ -0,0 +1,26 @@
+import React from 'react';
+
+import { LocalizerType } from '../../types/Util';
+
+type Props = {
+  count: number;
+  i18n: LocalizerType;
+};
+
+export class LastSeenIndicator extends React.Component<Props> {
+  public render() {
+    const { count, i18n } = this.props;
+
+    const message =
+      count === 1
+        ? i18n('unreadMessage')
+        : i18n('unreadMessages', [String(count)]);
+
+    return (
+      <div className="module-last-seen-indicator">
+        <div className="module-last-seen-indicator__bar" />
+        <div className="module-last-seen-indicator__text">{message}</div>
+      </div>
+    );
+  }
+}