refactor: Avatar widget

lib/widgets/avatar.dart

@@ -18,9 +18,9 @@ class Avatar extends StatelessWidget {
   final Client? client;
   final double fontSize;
 
-  const Avatar(
+  const Avatar({
     this.mxContent,
-    this.name, {
+    this.name,
     this.size = defaultSize,
     this.onTap,
     this.client,

lib/widgets/contacts_list.dart

@@ -87,7 +87,12 @@ class _ContactListTile extends StatelessWidget {
               height: Avatar.defaultSize,
               child: Stack(
                 children: [
-                  Center(child: Avatar(avatarUrl, displayname)),
+                  Center(
+                    child: Avatar(
+                      mxContent: avatarUrl,
+                      name: displayname,
+                    ),
+                  ),
                   Align(
                     alignment: Alignment.bottomRight,
                     child: Icon(