add 2D physics (use box2d), fixed some little bugs

ExampleApp/Src/RandomColor.cs

@@ -0,0 +1,26 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+using Prism;
+
+namespace Example
+{
+    class RandomColor : Entity
+    {
+        void OnCreate()
+        {
+            Random random = new Random();
+
+            MeshComponent meshComponent = GetComponent<MeshComponent>();
+            MaterialInstance material = meshComponent.Mesh.GetMaterial(0);
+            float r = (float)random.NextDouble();
+            float g = (float)random.NextDouble();
+            float b = (float)random.NextDouble();
+            material.Set("u_AlbedoColor", new Vec3(r, g, b));
+        }
+
+    }
+}