Rework of Supervoxel Classes

This is a reworking of my Supervoxel class and its corresponding octree
Renamed OctreePointCloudSupervoxel class to OctreePointCloudAdjacency - now it is general, not just for supervoxels
Renamed Supervoxels  to SupervoxelClustering. Now works better, allows for a transform etc..
Extended and updated the demonstration supervoxel program in examples/segmentation.
Also added a simple function in PCLVisualizer to check for existence of an id in the actor map