add unread indicator

lib/src/unread_indicator.dart

@@ -0,0 +1,28 @@
+import 'package:flutter/material.dart';
+import 'package:stream_chat/stream_chat.dart';
+import 'package:stream_chat_flutter/src/stream_chat_theme.dart';
+
+class UnreadIndicator extends StatelessWidget {
+  const UnreadIndicator({
+    Key key,
+    @required this.channel,
+  }) : super(key: key);
+
+  final Channel channel;
+
+  @override
+  Widget build(BuildContext context) {
+    return Padding(
+      padding: const EdgeInsets.only(left: 8.0),
+      child: CircleAvatar(
+        backgroundColor:
+            StreamChatTheme.of(context).channelPreviewTheme.unreadCounterColor,
+        radius: 6,
+        child: Text(
+          '${channel.state.unreadCount}',
+          style: TextStyle(fontSize: 8),
+        ),
+      ),
+    );
+  }
+}