Refactor project from Ghost.App to Ghost.Editor

Changed the project structure to reflect a shift from `Ghost.App` to `Ghost.Editor`, updating namespaces and class names throughout.

Changed the application class in `App.xaml` and `App.xaml.cs` from `GhostApplication` to `EditorApplication`.

Changed several service interfaces to reside under `Ghost.Editor.Services.Contracts`, including `IInspectorService`, `INotificationService`, and `IProgressService`.

Added `InspectorView` and `InspectorViewModel` classes to manage inspector functionality.

Added `NavigationTabView` and `NavigationTabPage` classes to facilitate navigation within the editor.

Enhanced `WorldNode` and `EntityNode` classes to support scene graph functionality, including serialization and entity management.

Updated the project file `Ghost.Editor.csproj` to reflect the new structure and removed old references.

Modified the solution file `GhostEngine.sln` to remove references to `Ghost.App` and include `Ghost.Editor`.

Updated unit tests to align with the new namespaces and project structure.

Ghost.Editor/AssetHandle/Asset.cs

@@ -0,0 +1,24 @@
+namespace Ghost.Editor.AssetHandle;
+
+public abstract class Asset
+{
+    /// <summary>
+    /// Get the Guid of the asset.
+    /// </summary>
+    public Guid GUID
+    {
+        get;
+    } = Guid.NewGuid();
+
+    /// <summary>
+    /// True if the asset is a folder, false if it is a file.
+    /// </summary>
+    public bool IsFolder
+    {
+        get;
+    }
+
+    internal void GenerateMetadata()
+    {
+    }
+}