Layout created for single screen app (#2)

lib/Utils/ViewState.dart

@@ -0,0 +1,20 @@
+import 'package:sealed_annotations/sealed_annotations.dart';
+
+@Sealed()
+abstract class ViewState {}
+
+class Idle implements ViewState {}
+
+class HasStarted implements ViewState {}
+
+class HasData implements ViewState {
+  final dynamic data;
+
+  HasData(this.data);
+}
+
+class HasError implements ViewState {
+  final String error;
+
+  HasError(this.error);
+}