Add Color record struct, small refactor, create a DaggerFramework.SceneGraph namespace.

Source/SceneGraph/Layer.cs

@@ -0,0 +1,21 @@
+using DaggerFramework.Rendering;
+
+namespace DaggerFramework.SceneGraph
+{
+    public abstract class Layer : IDrawable
+    {
+        public Scene Scene { get; set; }
+        public InputHandler Input { get; set; }
+
+        public void Draw(Renderer renderer) => OnDraw(renderer);
+
+        public void Start() => OnStart();
+        public void Update(double dt) => OnUpdate(dt);
+        public void ReceiveInput(InputHandler input) => OnInput(input);
+
+        protected virtual void OnStart() { }
+        protected virtual void OnUpdate(double dt) { }
+        protected virtual void OnInput(InputHandler input) { }
+        protected abstract void OnDraw(Renderer renderer);
+    }
+}