Inherit StatisticalOutlierRemoval<PCLPointCloud2> from FilterIndices

[stefanbuettner]

Hey all,

recently I was very happy to see that there are specializations of many algorithms for PCLPointCloud2. However, the StatisticalOutlierRemoval<PCLPointCloud2> class inherits from Filter<PCLPointCloud2> as opposed to the StatisticalOutlierRemoval<PointT> which inherits from FilterIndices<PointT>. In contrast to the Filter class, FilterIndices supports keeping the cloud organized apart from only returning an index list of the good points, of course.
This PR suggests a change from the Filter<PCLPointCloud2> base class to the FilterIndices<PCLPointCloud2> base class allowing to keep the point cloud organized and to filter only the indices.

What do you think?
I still need to squash.

Best,
Stefan

[taketwo]

FilterIndices is a subclass of Filter, so we should not be breaking anyone's code. LGTM.