Show Buttons in entity editor

- ScriptEngine: Added HasCustomAttribute- extension method
- ScriptEngine: Added Application class

ScriptCore/Editor/HideInEditorAttribute.cs

@@ -0,0 +1,11 @@
+using System;
+
+namespace GlitchyEngine.Editor;
+
+/// <summary>
+/// Specifies, that the field should not be visible in the editor.
+/// </summary>
+[AttributeUsage(AttributeTargets.Field)]
+public sealed class HideInEditorAttribute : Attribute
+{
+}