Open file from Explorer with association works

Major code refactor in Open, Save and Recent pages and VM
Main page automatically opens a sub page depending on context

ModernKeePass/ViewModels/SaveVm.cs

@@ -0,0 +1,33 @@
+using System.ComponentModel;
+using Windows.UI.Xaml;
+using ModernKeePass.Common;
+
+namespace ModernKeePass.ViewModels
+{
+    public class SaveVm: INotifyPropertyChanged
+    {
+        public bool IsSaveEnabled
+        {
+            get
+            {
+                var app = (App)Application.Current;
+                return app.Database.Status == DatabaseHelper.DatabaseStatus.Opened;
+            }
+        }
+
+        public event PropertyChangedEventHandler PropertyChanged;
+        private void NotifyPropertyChanged(string propertyName)
+        {
+            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
+        }
+
+        public void Save(bool close = true)
+        {
+            var app = (App)Application.Current;
+            app.Database.Save();
+            if (!close) return;
+            app.Database.Close();
+            NotifyPropertyChanged("IsSaveEnabled");
+        }
+    }
+}