Some refactoring of code. and some cleanups

Source/Game/Collision/BoundingIntervalHierarchy.cs

@@ -19,7 +19,6 @@ using Framework.GameMath;
 using System;
 using System.Collections.Generic;
 using System.IO;
-using System.Linq;
 using System.Runtime.InteropServices;
 
 namespace Game.Collision

Source/Game/Collision/BoundingIntervalHierarchyWrap.cs

@@ -16,7 +16,6 @@
  */
 
 using Framework.GameMath;
-using System;
 using System.Collections.Generic;
 
 namespace Game.Collision

Source/Game/Collision/DynamicTree.cs

@@ -16,7 +16,6 @@
  */
 
 using Framework.GameMath;
-using System.Collections.Generic;
 
 namespace Game.Collision
 {

Source/Game/Collision/Models/IModel.cs

@@ -16,15 +16,14 @@
  */
 
 using Framework.GameMath;
-using System.Collections.Generic;
 using Framework.Constants;
 
 namespace Game.Collision
 {
     public class IModel
     {
-        public virtual Vector3 getPosition() { return default(Vector3); }
-        public virtual AxisAlignedBox getBounds() { return default(AxisAlignedBox); }
+        public virtual Vector3 getPosition() { return default; }
+        public virtual AxisAlignedBox getBounds() { return default; }
 
         public virtual bool IntersectRay(Ray ray, ref float maxDist, bool stopAtFirstHit, PhaseShift phaseShift, ModelIgnoreFlags ignoreFlags) { return false; }
         public virtual bool IntersectRay(Ray ray, ref float distance, bool stopAtFirstHit, ModelIgnoreFlags ignoreFlags) { return false; }

Source/Game/Collision/RegularGrid2D.cs

@@ -18,7 +18,6 @@
 using Framework.GameMath;
 using System;
 using System.Collections.Generic;
-using System.Collections.Concurrent;
 
 namespace Game.Collision
 {