Make fixes for VTK 6

This fixes compilation errors encountered when building PCL
against VTK 6 (from the current git master). The changes are
based on the recommendations in the VTK 6 migration guide [1].

This closes issue #199.

[1] http://www.vtk.org/Wiki/VTK/VTK_6_Migration_Guide
More VTK 6 fixes
Updates for VTK6 - avoiding Image_viewer_

LG
VTK6 fixes.

Conflicts:
	apps/3d_rec_framework/include/pcl/apps/3d_rec_framework/pc_source/mesh_source.h
cmake.in fix for vtk6, using VTK_LIBRARIES
Use VTK_FILE if on version 6
Fix: why remove the ImageViewer from this class ??
vtk 6 doesn't have USE_VTK_COCOA and USE_VTK_CARBON, and it doesn't support carbon anymore
Updates for VTK6 - avoiding Image_viewer_

LG
Fix: why remove the ImageViewer from this class ??
Fix: VTK 6 is unable to work with Qt5!
Fix: put back VTK libraries as they were, no need for extra stuff!
Update: On VTK 6 and greater QVTK was split among several modules
Fix: for VTK 6
Revert "Fix: put back VTK libraries as they were, no need for extra stuff!"

This reverts commit 0f3c31cb79e9e3f2d2c73278887439a6b2c14089.
Fix: replace QVTK with ${QVTK_LIBRARY} to keep it working
Fix: replace VTK_MAJOR_VERSION <= 5 with VTK_MAJOR_VERSION < 6

This makes is it easier to find and also faster to evaluate