Modernize the repr() for vtk-python objects
The new style for repr(o) is similar to PySide and numpy. For example:
<vtkmodules.vtkCommonCore.vtkObject(0xbd306710) at 0x69252b820>
Or, for objects of type vtkVariant, vtkVector3f, etc:
vtkmodules.vtkCommonCore.vtkVariant("hello")
vtkmodules.vtkCommonDataModel.vtkVector3f([1.0, 2.0, 3.0])
In comparison, the old style looked like a C-style cast:
(vtkmodules.vtkCommonCore.vtkObject)0x7f7604423940
(vtkmodules.vtkCommonDataModel.vtkVector3f)[1.0, 2.0, 3.0]