Couple UI Fixes (#255)

- Disabled UI navigation cache for all pages.
- Restore the renderer<>composer page animation back.
- IdlePage functionality into mail list page.
- Couple bugfixes.

Wino.Mail/Views/MailListPage.xaml

@@ -20,6 +20,7 @@
     xmlns:ui="using:Microsoft.Toolkit.Uwp.UI"
     xmlns:viewModelData="using:Wino.Mail.ViewModels.Data"
     xmlns:wino="using:Wino"
+    xmlns:converters="using:Wino.Converters"
     x:Name="root"
     Loaded="MailListPageLoaded"
     mc:Ignorable="d">
@@ -478,6 +479,7 @@
                                 x:Name="SelectionModeToggle"
                                 Grid.Column="1"
                                 Checked="SelectionModeToggleChecked"
+                                IsChecked="{x:Bind ViewModel.IsMultiSelectionModeEnabled, Mode=TwoWay}"
                                 Style="{StaticResource TopCommandBarToggleButtonStyle}"
                                 Unchecked="SelectionModeToggleUnchecked">
                                 <ToggleButton.Content>
@@ -807,13 +809,28 @@
             </Grid>
         </Border>
 
-        <!--  Mail Rendering Frame  -->
-        <Frame
-            x:Name="RenderingFrame"
-            Grid.Column="1"
-            IsNavigationStackEnabled="False" />
+        <Grid Grid.Column="1" x:Name="RenderingGrid">
+            <!--  Mail Rendering Frame  -->
+            <Frame x:Name="RenderingFrame" IsNavigationStackEnabled="False"  />
 
+            <!--  No Mail Selected Message  -->
+            <StackPanel
+                x:Name="NoMailSelectedPanel"
+                Opacity="0.5"
+                Spacing="6"
+                HorizontalAlignment="Center"
+                VerticalAlignment="Center">
 
+                <controls:WinoFontIcon Icon="Mail" FontSize="80" />
+
+                <TextBlock
+                    HorizontalAlignment="Center"
+                    FontSize="31"
+                    Text="{x:Bind ViewModel.SelectedMessageText, Mode=OneWay}"
+                    Style="{StaticResource SubheaderTextBlockStyle}"
+                    x:Name="CountTextBlock" />
+            </StackPanel>
+        </Grid>
 
 
         <VisualStateManager.VisualStateGroups>