Make some color methods consistent.

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: I89fee8eb4902e0847114b068374c3bff0bf10b9d
Merge topic 'Virtualize_Color_Methods-rel' into master

293e5386 Make some color methods consistent.