Make StartPage better on phones

Author: golf1052

Signal-Windows/Views/StartPage.xaml

@@ -24,9 +24,21 @@
     </Page.Resources>
 
     <Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
+        <VisualStateManager.VisualStateGroups>
+            <VisualStateGroup>
+                <VisualState>
+                    <VisualState.StateTriggers>
+                        <AdaptiveTrigger MinWindowWidth="640"/>
+                    </VisualState.StateTriggers>
+                    <VisualState.Setters>
+                        <Setter Target="TitleTextBlock.FontSize" Value="46"/>
+                    </VisualState.Setters>
+                </VisualState>
+            </VisualStateGroup>
+        </VisualStateManager.VisualStateGroups>
         <StackPanel HorizontalAlignment="Center" VerticalAlignment="Center">
             <Image Source="ms-appx:///Assets/logo-idea-2.png" Width="256"/>
-            <TextBlock Text="Welcome to Signal for Windows" Foreground="White" FontSize="46" FontWeight="Light" HorizontalAlignment="Center" Margin="0,50,0,0"/>
+            <TextBlock x:Name="TitleTextBlock" Text="Welcome to Signal for Windows" Foreground="White" FontSize="24" FontWeight="Light" HorizontalAlignment="Center" Margin="0,50,0,0"/>
             <Button x:Name="RegisterButton" HorizontalAlignment="Center" Foreground="#2190EA" Background="White" Content="Register a new Signal account" Margin="0,50,0,0" Click="RegisterButton_Click"/>
             <Button x:Name="LinkButton" HorizontalAlignment="Center" Foreground="#2190EA" Background="White" Content="Link to an existing Signal account" Margin="0,20,0,0" Click="LinkButton_Click"/>
         </StackPanel>