[visualization] add Scalar template variable to RegistrationVisualizer

[keineahnung2345]

No description provided.

[mvieth]

Would you explain a bit more what these changes are for? Was it previously not possible to use the visualizer with all registration classes?

[keineahnung2345]

After add Scalar template variable to NormalDistributionsTransform, I tried to use it as NormalDistributionsTransform<PointSource, PointTarget, double> with RegistrationVisualizer, and it failed at setRegistration (pcl::Registration<PointSource, PointTarget> &registration). So I realized that RegistrationVisualizer should also have a Scalar template variable to make it compilable.

[mvieth]

Thanks