Implement refactored VoxelGrid

* Inherit from TransformFilter and GridFilterBase

* Complete the API of old VoxelGrid

* Implement new way for checking unsigned int overflow

* Improve performance by switching from sorting to unordered_map

Author: tin1254

filters/CMakeLists.txt

@@ -90,6 +90,7 @@ set(experimental_incs
   "include/pcl/${SUBSYS_NAME}/experimental/functor_filter.h"
   "include/pcl/${SUBSYS_NAME}/experimental/grid_filter_base.h"
   "include/pcl/${SUBSYS_NAME}/experimental/transform_filter.h"
+  "include/pcl/${SUBSYS_NAME}/experimental/voxel_grid.h"
 )
 
 set(impl_incs