[vtkusers] vtkFLTK 0.6.0 Magic update release

[Sean McInerney]

The 0.6.0 release of vtkFLTK features some minor API changes enabling 
some major magic. The Interactor Start() method is now fully implemented 
and will, in fact, start the FLTK event loop as well as adding an 
ExitEvent Observer which may be used to override the usual behavior of 
TerminateApp. What this means for developers is vastly improved 
transparency for writing either the VTK visualization pipeline or FLTK 
graphical interface parts of an application. Beyond a simple header 
inclusion, one need never refer to any vtkFLTK class specializations in 
order to use them ... like magic!

The Magic(tm) happens with inclusion of the vtkFLTK Instantiator and 
causes all RenderWindow and Interactor instances to be vtkFLTK 
specializations. Merely including 'vtkFLTKInstantiator.h' into any VTK 
C++ example will ensure its use of vtkFLTK and, most importantly, the 
FLTK event loop. This allows easy addition of FLTK widget interfaces to 
existing code. For illustration of this behind the scenes instantiation, 
please see the 'Simple' and 'Simple2' examples.

-Sean