Export organized clouds

[matlabbe]

When exporting 3D clouds (File->Export 3D clouds), if Regenerate clouds=true, Voxel=0, maximum depth=0 and Assemble clouds=false, exported clouds should be organized. This can be done easily by removing removeNaNFromPointCloud() here. Just make sure that other stuff using this method are not assuming that there are no NaN values in the cloud returned.

See this post for the convention about detecting organized/dense clouds: http://www.pcl-users.org/warning-is-dense-misused-td2029417.html

[matlabbe]

Added in c6a46a7