Remove "global" from all calls to `addCoordinateSystem`

This makes the tutorial compatible with both PCL <= 1.7.1 and the
current master.

See the discussion on dev list: http://www.pcl-developers.org/pcl-visualizer-demo-cpp-compilation-error-and-solution-td5709431.html
Merge pull request #614 from taketwo/fix-pcl-visualizer-tutorial

Remove "global" from all calls to `addCoordinateSystem`