[vtkusers] general purpose streamline parameters

[Steve Kirstukas]

Whether or not streamlines appear seems to be very sensitive to the SetStepLength 
parameter.

Do you have any suggestions as to general purpose (not neccessarily most efficient) 
values to use for:
   SetMaximumPropagationTime parameter
   SetIntegrationStepLength parameter
   SetStepLength parameter

Thanks, Steve