Some revisions to grass brush.

- Made some changes to the way I check for deleting instances.
- Added a new bounding box check for painting grass.
- Made GetNewGrassBounds return a bounding box instead of our parameters
- Added new Expand method to bounding box util
- Added instance radius check and instance brush check to project form for possible future instance types (Props)
- Added grass brush gizmo
- Updated gui for grass instance batch panel
- Fixed bug with GoToPosition (with bounds)

CodeWalker.Core/Utils/BoundingBoxes.cs

@@ -30,5 +30,10 @@ namespace CodeWalker.Core.Utils
             var extents = (box.Maximum - box.Minimum) * 0.5F;
             return extents.Length();
         }
+
+        public static BoundingBox Expand(this BoundingBox b, float amount)
+        {
+            return new BoundingBox(b.Minimum - Vector3.One * amount, b.Maximum + Vector3.One * amount);
+        }
     }
 }