Add roscreate-pkg skel for sr_pcl_tracking
Add example from ROS.org.
Add VoxGrid filter example.
Add shell for tracker node.
Start bringing in the Tracker code.

Pull in libs and start cloud_cb by just doing the downsample.
Feed the tracker.
Add a Z pass through filter.
Add srv to start tracker.

track_nearest service and publish the particle cloud. This doesn't seem to be
working quite right yet.
Publish the result cloud.
Seperate byDistance and byCentered
Start on load and save services.
Fix srv advertisment and stub in load cb.
Bit of error checking on the requests.
Add load_cloud srv and find that cloud to track.

This pulls in the last of the code from the prototype. So next it is all
making the interface better, exposing lots of params, refactoring and testing.
Tweak error handling.
Add some more error checks on ref dir.
List references service.
Pull out the extention string for reference files.
Better topic naming.
Fix warning.