In order to use functions like SetTableValue(2, "Blue") in a lookup table
  or other SetColors in derived classes in the same manner,
  these methods should be virtual.
This commit just makes the relevant Set methods virtual.
In the case of vtkProperty, the definition of SetColor(double a[3]) has
  been moved into vtkProperty.cxx, the rationale is that, in VTK classes,
  definitions occur in the implementation file not the header file.

Change-Id: I6ad8d0019785faed1f7cb157192fdcc2f2d70c34
Signed-off-by: Andrew Maclean <andrew.amaclean@gmail.com>