bugfix: in-place filtering with VoxelGrid

[dseredyn]

You should not use in-place filtering with VoxelGrid as stated in
http://www.pcl-users.org/strange-effect-of-the-downsampling-td3857829.html

[VictorLamoine]

I think I'll soon integrate this tool as part of the PCL library through something like a uniformCloudFromMesh function.

I also don't understand the point of the voxel grid. What is the point of upscaling a cloud to a certain point count and then down-sample it to an unknown point count ?!

[dseredyn]

The images show the reason for using the voxel grid. They show point clouds generated from a cube mesh. Each point cloud have ~10000 points. The second one is generated from point cloud with 100000 points and down-sampled with the voxel grid. Is has more 'structured' distribution.