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

Source/SceneGraph/Entities/Drawable2d.cs

@@ -0,0 +1,15 @@
+using DaggerFramework.Rendering;
+
+namespace DaggerFramework.SceneGraph
+{
+    public abstract class Drawable2d : Entity2d, IDrawable
+    {
+        public void Draw(Renderer renderer)
+        {
+            renderer.SetTransform(Position);
+            OnDraw(renderer);
+        }
+
+        public abstract void OnDraw(Renderer renderer);
+    }
+}