New port: math/vtk8: Visualization toolkit (repocopy of math/vtk6 with modifications)

Changes against math/vtk6:

• Use DISTVERSION
• Update COMMENT
• Add to USES
• Remove the SHARED option: all libraries should be shared, no need for the option to do otherwise
• Remove the PYTHON option: python binding should be a separate port
• Modernize the port: use helpers instead of .if/.endif
• Use autoplist: too many files with too complex dependencies on options
• Update USE_QT to include missing parts