App Settings: transition type and length picker

Cut/Fade/Move and a 100-2000 ms length, bound to the view model; changes save with the layout.
Test: TransitionPickerTests. Not pushed.

Controls/OverlayHost.xaml

@@ -2,7 +2,8 @@
              xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
              xmlns:Helpers="clr-namespace:ytLive.Helpers"
-             xmlns:Models="clr-namespace:ytLive.Models">
+             xmlns:Models="clr-namespace:ytLive.Models"
+             xmlns:services="clr-namespace:ytLive.Services">
         <Grid Grid.RowSpan="3"
               Visibility="{Binding IsAnyOverlayOpen, Converter={StaticResource BoolToVis}}">
             <Button Background="#99000000" BorderThickness="0" Cursor="Hand"
@@ -55,6 +56,17 @@
                             <ComboBoxItem Content="Phone (Vertical Rectangle)" Tag="{x:Static Models:ZoomShape.VerticalRectangle}"/>
                             <ComboBoxItem Content="Tablet (Horizontal Rectangle)" Tag="{x:Static Models:ZoomShape.HorizontalRectangle}"/>
                         </ComboBox>
+                        <TextBlock Text="Scene Transition" Style="{StaticResource YtLabel}" Margin="0,12,0,4"/>
+                        <ComboBox Style="{StaticResource YtComboBox}" SelectedValue="{Binding SelectedTransitionType}" SelectedValuePath="Tag">
+                            <ComboBoxItem Content="Cut" Tag="{x:Static services:TransitionType.Cut}"/>
+                            <ComboBoxItem Content="Fade" Tag="{x:Static services:TransitionType.Fade}"/>
+                            <ComboBoxItem Content="Move" Tag="{x:Static services:TransitionType.Move}"/>
+                        </ComboBox>
+                        <TextBlock Style="{StaticResource YtLabel}" Margin="0,8,0,4">
+                            <Run Text="Transition length: "/><Run Text="{Binding TransitionDurationMs, StringFormat={}{0:0} ms}"/>
+                        </TextBlock>
+                        <Slider Minimum="100" Maximum="2000" TickFrequency="50" IsSnapToTickEnabled="True"
+                                Value="{Binding TransitionDurationMs, Mode=TwoWay}"/>
                     </StackPanel>
 
                     <!-- Report Bug -->