Major changes in MainPage: now is layout dependant (with a base, to prepare for Settings)

Main sub pages also changed to better work with Main (but needs improvement)
Added a Settings Page stub

ModernKeePass/Pages/MainPageFrames/RecentDatabasesPage.xaml.cs

@@ -0,0 +1,37 @@
+using System;
+using Windows.UI.Xaml;
+using Windows.UI.Xaml.Controls;
+using Windows.UI.Xaml.Navigation;
+using ModernKeePass.ViewModels;
+
+// Pour en savoir plus sur le modèle d'élément Page vierge, consultez la page http://go.microsoft.com/fwlink/?LinkId=234238
+
+namespace ModernKeePass.Pages
+{
+    /// <summary>
+    /// Une page vide peut être utilisée seule ou constituer une page de destination au sein d'un frame.
+    /// </summary>
+    public sealed partial class RecentDatabasesPage
+    {
+        private Frame _mainFrame;
+
+        public RecentVm Model => (RecentVm)DataContext;
+
+        public RecentDatabasesPage()
+        {
+            InitializeComponent();
+        }
+
+        protected override void OnNavigatedTo(NavigationEventArgs e)
+        {
+            base.OnNavigatedTo(e);
+            _mainFrame = e.Parameter as Frame;
+        }
+        
+        private void OpenDatabaseUserControl_OnValidationChecking(object sender, EventArgs e)
+        {
+            var app = (App)Application.Current;
+            app.Database.DatabaseFile = Model.SelectedItem.DatabaseFile;
+        }
+    }
+}