Add built-in HelixViewer for 3d models

QuickLook.Plugin/QuickLook.Plugin.HelixViewer/HelixPanel.xaml

@@ -0,0 +1,24 @@
+<UserControl x:Class="QuickLook.Plugin.HelixViewer.HelixPanel"
+             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+             xmlns:helix="clr-namespace:HelixToolkit.Wpf;assembly=HelixToolkit.Wpf"
+             xmlns:local="clr-namespace:QuickLook.Plugin.HelixViewer"
+             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+             d:DesignHeight="450"
+             d:DesignWidth="800"
+             mc:Ignorable="d">
+    <Grid>
+        <helix:HelixViewport3D x:Name="viewer"
+                               CameraRotationMode="Turnball"
+                               ShowViewCube="False"
+                               ZoomAroundMouseDownPoint="True"
+                               ZoomExtentsWhenLoaded="true">
+            <ModelVisual3D x:Name="modelVisual" />
+            <helix:DefaultLights />
+            <helix:HelixViewport3D.RotateGesture>
+                <MouseGesture MouseAction="LeftClick" />
+            </helix:HelixViewport3D.RotateGesture>
+        </helix:HelixViewport3D>
+    </Grid>
+</UserControl>