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/NewDatabasePage.xaml.cs

@@ -0,0 +1,48 @@
+using System;
+using System.Collections.Generic;
+using Windows.Storage.Pickers;
+using Windows.UI.Xaml;
+using Windows.UI.Xaml.Controls;
+using Windows.UI.Xaml.Navigation;
+using ModernKeePass.Events;
+using ModernKeePass.ViewModels;
+
+// The Blank Page item template is documented at http://go.microsoft.com/fwlink/?LinkId=234238
+
+namespace ModernKeePass.Pages
+{
+    /// <summary>
+    /// An empty page that can be used on its own or navigated to within a Frame.
+    /// </summary>
+    public sealed partial class NewDatabasePage
+    {
+        private Frame _mainFrame;
+
+        public NewVm Model => (NewVm)DataContext;
+
+        public NewDatabasePage()
+        {
+            InitializeComponent();
+        }
+
+        protected override void OnNavigatedTo(NavigationEventArgs e)
+        {
+            base.OnNavigatedTo(e);
+            _mainFrame = e.Parameter as Frame;
+        }
+
+        private async void ButtonBase_OnClick(object sender, RoutedEventArgs e)
+        {
+            var savePicker = new FileSavePicker
+            {
+                SuggestedStartLocation = PickerLocationId.DocumentsLibrary,
+                SuggestedFileName = "New Database"
+            };
+            savePicker.FileTypeChoices.Add("KeePass 2.x database", new List<string> { ".kdbx" });
+
+            var file = await savePicker.PickSaveFileAsync();
+            if (file == null) return;
+            Model.OpenFile(file);
+        }
+    }
+}