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.UnitTest/Package.appxmanifest

@@ -0,0 +1,51 @@
+<?xml version="1.0" encoding="utf-8"?>
+
+<Package
+  xmlns="http://schemas.microsoft.com/appx/manifest/foundation/windows10"
+  xmlns:mp="http://schemas.microsoft.com/appx/2014/phone/manifest"
+  xmlns:uap="http://schemas.microsoft.com/appx/manifest/uap/windows10"
+  xmlns:rescap="http://schemas.microsoft.com/appx/manifest/foundation/windows10/restrictedcapabilities"
+  IgnorableNamespaces="uap rescap">
+
+  <Identity
+    Name="7329af59-6d61-48e9-9041-8f2d3d23696b"
+    Publisher="CN=Misaki"
+    Version="1.0.0.0" />
+
+  <mp:PhoneIdentity PhoneProductId="7329af59-6d61-48e9-9041-8f2d3d23696b" PhonePublisherId="00000000-0000-0000-0000-000000000000"/>
+
+  <Properties>
+    <DisplayName>Ghost.UnitTest</DisplayName>
+    <PublisherDisplayName>Misaki</PublisherDisplayName>
+    <Logo>Assets\StoreLogo.png</Logo>
+  </Properties>
+
+  <Dependencies>
+    <TargetDeviceFamily Name="Windows.Universal" MinVersion="10.0.17763.0" MaxVersionTested="10.0.19041.0" />
+    <TargetDeviceFamily Name="Windows.Desktop" MinVersion="10.0.17763.0" MaxVersionTested="10.0.19041.0" />
+  </Dependencies>
+
+  <Resources>
+    <Resource Language="x-generate"/>
+  </Resources>
+
+  <Applications>
+    <Application Id="App"
+      Executable="$targetnametoken$.exe"
+      EntryPoint="$targetentrypoint$">
+      <uap:VisualElements
+        DisplayName="Ghost.UnitTest"
+        Description="Ghost.UnitTest"
+        BackgroundColor="transparent"
+        Square150x150Logo="Assets\Square150x150Logo.png"
+        Square44x44Logo="Assets\Square44x44Logo.png">
+        <uap:DefaultTile Wide310x150Logo="Assets\Wide310x150Logo.png" />
+        <uap:SplashScreen Image="Assets\SplashScreen.png" />
+      </uap:VisualElements>
+    </Application>
+  </Applications>
+
+  <Capabilities>
+    <rescap:Capability Name="runFullTrust" />
+  </Capabilities>
+</Package>