Add starter project for chapter 4

Chapter04/Start/MyMediaCollection/ViewModels/BindableBase.cs

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+using System.ComponentModel;
+using System.Runtime.CompilerServices;
+
+namespace MyMediaCollection.ViewModels
+{
+    public class BindableBase : INotifyPropertyChanged
+    {
+        public event PropertyChangedEventHandler PropertyChanged;
+
+        protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
+        {
+            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
+        }
+
+        protected bool SetProperty<T>(ref T originalValue, T newValue, [CallerMemberName] string propertyName = null)
+        {
+            if (Equals(originalValue, newValue))
+            {
+                return false;
+            }
+
+            originalValue = newValue;
+            OnPropertyChanged(propertyName);
+
+            return true;
+        }
+    }
+}