add choose user pages

lib/src/stream_chat_theme.dart

@@ -218,6 +218,7 @@ class StreamChatThemeData {
     final accentColor = Color(0xff006cff);
     final isDark = theme.brightness == Brightness.dark;
     return StreamChatThemeData(
+      secondaryColor: Color(0xffEAEAEA),
       accentColor: accentColor,
       primaryColor: isDark ? Colors.black : Colors.white,
       primaryIconTheme: IconThemeData(

lib/src/user_avatar.dart

@@ -55,9 +55,7 @@ class UserAvatar extends StatelessWidget {
                       errorWidget: (_, __, ___) {
                         return Center(
                           child: Text(
-                            user.extraData?.containsKey('name') ?? false
-                                ? user.extraData['name'][0]
-                                : '',
+                            user.name[0],
                             style: TextStyle(
                               color: Colors.white,
                               fontWeight: FontWeight.bold,