Add `vtkmodules` package

The fact that vtk package imports all of VTK at initialization time has been a headache for ParaView. That has resulted in ParaView copying vtk package into its own paraview package which has resulted in other complications.

This MR provides a solution to support traditional vtk package together with a new vtkmodules package that includes all the modules in traditional vtk package without the initialization code. vtk package now simply "forwards" to vtkmodules package and hence avoid duplication.