Add wallpapers to start new chat pages

lib/views/new_group.dart

@@ -95,6 +95,9 @@ class _NewGroupState extends State<_NewGroup> {
             value: publicGroup,
             onChanged: (bool b) => setState(() => publicGroup = b),
           ),
+          Expanded(
+            child: Image.asset("assets/new_group_wallpaper.png"),
+          ),
         ],
       ),
       floatingActionButton: FloatingActionButton(

lib/views/new_private_chat.dart

@@ -228,6 +228,10 @@ class _NewPrivateChatState extends State<_NewPrivateChat> {
               ),
             ),
           Divider(height: 1),
+          if (foundProfiles.isEmpty || correctMxId)
+            Expanded(
+              child: Image.asset("assets/private_chat_wallpaper.png"),
+            ),
         ],
       ),
       floatingActionButton: FloatingActionButton(