Unimplemented python binding in ViewControl

**Is your feature request related to a problem? Please describe.**
Currently, I'm trying to preserve the camera view when changing between `o3d.visualization.Visualizer` and `o3d.visualization.VisualizerWithVertexSelection` in python.

I am looking at the function [ConvertToViewParameters and ConvertFromViewParameters](https://github.com/intel-isl/Open3D/blob/75dd3674511afc05dd752d9b12cb474042781bde/cpp/open3d/visualization/visualizer/ViewControl.h#L70-L71) which should do what I needed and already implemented in CPP, it's just missing binding in Python

**Describe the solution you'd like**
Can someone help me implement this binding to [pybind/visualization/viewcontrol.cpp](https://github.com/intel-isl/Open3D/blob/master/cpp/pybind/visualization/viewcontrol.cpp)

If possible, make the python binding more complete for this file.. Currently the [python binding](http://www.open3d.org/docs/release/python_api/open3d.visualization.ViewControl.html#open3d.visualization.ViewControl) is lacking behind the [c++ implementation](http://www.open3d.org/docs/release/cpp_api/classopen3d_1_1visualization_1_1_view_control.html)

**Describe alternatives you've considered**
Maybe I'll do this myself if nobody pick this up and when I have the time

**Additional context**