big refactorization of the include headers for pcl_visualization. Major
changes include: forward declarations for most classes used in headers,
and inclusion of real headers (e.g., VTK) in the cpp implementations;
fixes for certain command line tools, apps and examples in PCL that were
not including the headers they were using correctly.
Merge pull request #143 from rbrusu/master

Big refactorization of the include headers for pcl_visualization to reduce compile time of VTK header includes.