Add Async image loading

Examples/Time Travel/SwiftUITimeTravel/TimeTravelView/TimeTravelBarView.swift

@@ -0,0 +1,25 @@
+import SwiftUI
+
+struct TimeTravelBarView : View {
+    
+    @EnvironmentObject var store: Store<TodoState>
+    
+    var body: some View {
+        let indexBinding = Binding<Double>(
+            getValue: { Double(self.store.currentStateIndex) },
+            setValue: { self.store.currentStateIndex = Int($0) })
+
+        return Slider(value: indexBinding, from: 0, through: Double(store.stateCount-1))
+            .background(Color.white)
+            .frame(height: 44.0, alignment: .bottom)
+            .padding()
+    }
+}
+
+#if DEBUG
+struct TimeTravelBarView_Previews : PreviewProvider {
+    static var previews: some View {
+        TimeTravelBarView()
+    }
+}
+#endif