ENH: update to new LandmarkRegistration

Now with interactive ThinPlate registration!
- uses real-time nonlinear transform updates
- compatible with transform visualization

Other improvments and upgrades, like VTKv6 support and
generalization of the plugin architecture.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23433 3bd1e089-480b-0410-8dfb-8563597acbee