Refactor MainWindow with MVVM

- Add MVVM structure(BaseViewModel)
- Create ViewModel for MainWindow
- Refactor MainWindow.xaml to support MVVM
- Move PublicAPI implementation from MainViewModel to PublicAPIInstance

Wox/ViewModel/BaseViewModel.cs

@@ -0,0 +1,50 @@
+using System;
+using System.Collections.Generic;
+using System.ComponentModel;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using System.Windows.Input;
+
+namespace Wox.ViewModel
+{
+    public class BaseViewModel : INotifyPropertyChanged
+    {
+
+        protected virtual void OnPropertyChanged(string propertyName)
+        {
+            if (null != this.PropertyChanged)
+            {
+                this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
+            }
+        }
+
+        public event PropertyChangedEventHandler PropertyChanged;
+    }
+
+    public class RelayCommand : ICommand
+    {
+
+        private Action _action;
+
+        public RelayCommand(Action action)
+        {
+            this._action = action;
+        }
+
+        public virtual bool CanExecute(object parameter)
+        {
+            return true;
+        }
+
+        public event EventHandler CanExecuteChanged;
+
+        public virtual void Execute(object parameter)
+        {
+            if (null != this._action)
+            {
+                this._action();
+            }
+        }
+    }
+}