Refactor application structure and add unit tests

Added:
- New `ProgressService` class for managing progress indicators.
- New `AssetDatabase`, `AssetOpenHandlerAttribute`, and `AsyncAssetOpenHandlerAttribute` classes for asset handling.
- `Ghost.UnitTest` project for unit testing with associated files and configurations.

Changed:
- `ActivationHandler` class to ensure correct handling of `LaunchActivatedEventArgs`.
- `App.xaml.cs` to register `INotificationService` and `IProgressService`, replacing `StackedNotificationService`.
- `OnLaunched` method in `App.xaml.cs` to correctly call `ActivationHandler.Handle(args)` and start the host.
- `INavigationAware` interface from internal to public for broader access.
- `EditorState.cs` to activate `EditorApplication` with the current service provider.
- Property names in `AssetItem` and `ExplorerItem` structs to `Name` and `FullName`.
- `NotificationService` class to implement `INotificationService` and refactor notification handling.
- `AssetPathToGlyphConverter` to handle file extensions consistently.
- Bindings in `ProjectPage.xaml` and `ProjectPage.xaml.cs` to use `FullName` instead of `Path`.
- `EngineEditorWindow` and `LandingWindow` classes to utilize new notification and progress services.
- `Logger` class to include a new method for logging errors with exceptions.

Updated:
- Manifest files and project files to reflect new structure and dependencies.
- Solution file `GhostEngine.sln` to include the new unit test project.
- Added several new test classes and methods in `UnitTests.cs`.

Ghost.App/View/Pages/EngineEditor/HierarchyPage.xaml

@@ -0,0 +1,43 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<Page
+    x:Class="Ghost.App.View.Pages.EngineEditor.HierarchyPage"
+    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:local="using:Ghost.App.View.Pages.EngineEditor"
+    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+    xmlns:sg="using:Ghost.Editor.SceneGraph"
+    mc:Ignorable="d">
+
+    <Page.Resources>
+        <DataTemplate x:Key="SceneTemplate" x:DataType="sg:SceneGraphNode">
+            <TreeViewItem
+                AutomationProperties.Name="{x:Bind Name}"
+                Background="{ThemeResource ControlSolidFillColorDefaultBrush}"
+                IsExpanded="True"
+                ItemsSource="{x:Bind Children}">
+                <StackPanel Orientation="Horizontal">
+                    <FontIcon FontSize="14" Glyph="&#xF159;" />
+                    <TextBlock Margin="10,0" Text="{x:Bind Name}" />
+                </StackPanel>
+            </TreeViewItem>
+        </DataTemplate>
+
+        <DataTemplate x:Key="EntityTemplate" x:DataType="sg:SceneGraphNode">
+            <TreeViewItem AutomationProperties.Name="{x:Bind Name}" ItemsSource="{x:Bind Children}">
+                <StackPanel Orientation="Horizontal">
+                    <FontIcon FontSize="14" Glyph="&#xF158;" />
+                    <TextBlock Margin="10,0" Text="{x:Bind Name}" />
+                </StackPanel>
+            </TreeViewItem>
+        </DataTemplate>
+    </Page.Resources>
+
+    <Grid Padding="4,6" Background="{ThemeResource LayerFillColorDefaultBrush}">
+        <TreeView ItemsSource="{x:Bind ViewModel.SceneList}">
+            <TreeView.ItemTemplateSelector>
+                <local:HierarchyTemplateSector EntityTemplate="{StaticResource EntityTemplate}" WorldTemplate="{StaticResource SceneTemplate}" />
+            </TreeView.ItemTemplateSelector>
+        </TreeView>
+    </Grid>
+</Page>