Fixed TabControl and Viewbox pages

samples/ControlCatalog/Pages/TabControlPage.xaml

@@ -1,4 +1,7 @@
-<UserControl xmlns="https://github.com/avaloniaui">
+<UserControl
+    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+    x:Class="ControlCatalog.Pages.TabControlPage"
+    xmlns="https://github.com/avaloniaui">
     <DockPanel>
         <TextBlock 
             DockPanel.Dock="Top" 
@@ -29,13 +32,13 @@
                     <TabItem Header="Arch">
                         <StackPanel Orientation="Vertical" Spacing="8">
                             <TextBlock>This is the first page in the TabControl.</TextBlock>
-                            <Image Source="resm:ControlCatalog.Assets.delicate-arch-896885_640.jpg" Width="300"/>
+                            <Image Source="/Assets/delicate-arch-896885_640.jpg" Width="300"/>
                         </StackPanel>
                     </TabItem>
                     <TabItem Header="Leaf">                       
                         <StackPanel Orientation="Vertical" Spacing="8">
                             <TextBlock>This is the second page in the TabControl.</TextBlock>
-                            <Image Source="resm:ControlCatalog.Assets.maple-leaf-888807_640.jpg" Width="300"/>
+                            <Image Source="/Assets/maple-leaf-888807_640.jpg" Width="300"/>
                         </StackPanel>
                     </TabItem>
                     <TabItem Header="Disabled" IsEnabled="False">

samples/ControlCatalog/Pages/TabControlPage.xaml.cs

@@ -26,13 +26,13 @@ namespace ControlCatalog.Pages
                     {
                         Header = "Arch",
                         Text = "This is the first templated tab page.",
-                        Image = LoadBitmap("resm:ControlCatalog.Assets.delicate-arch-896885_640.jpg?assembly=ControlCatalog"),
+                        Image = LoadBitmap("avares://ControlCatalog/Assets/delicate-arch-896885_640.jpg"),
                     },
                     new TabItemViewModel
                     {
                         Header = "Leaf",
                         Text = "This is the second templated tab page.",
-                        Image = LoadBitmap("resm:ControlCatalog.Assets.maple-leaf-888807_640.jpg?assembly=ControlCatalog"),
+                        Image = LoadBitmap("avares://ControlCatalog/Assets/maple-leaf-888807_640.jpg"),
                     },
                     new TabItemViewModel
                     {

samples/ControlCatalog/Pages/ViewboxPage.xaml

@@ -1,5 +1,6 @@
 <UserControl xmlns="https://github.com/avaloniaui"
-             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             x:Class="ControlCatalog.Pages.ViewboxPage">
     <UserControl.Resources>
         <StreamGeometry x:Key="Acorn">
             F1 M 16.6309,18.6563C 17.1309,