use test driver & factory for interactive test mode
(prior change to test was unnecessary)

In InteractiveChartXYZ, initialize SceneWidth & SceneHeight
to 0 in constructor.  This eliminates the need for an overloaded
SetScene function.

use static cast instead of C style cast in vtkChartXYZ.

make vtkAxis::NiceNumber a static function to reduce code duplication.

Change-Id: Ifa8674baed7c7a0ea4d94caa2570c25366f1b657