Support MONAI interfaces for image information

As suggested by @aylward in #1, support MONAI Python dictionary interfaces for image information like origin, spacing, etc :+1:

> 1) You and others created some nice python helper functions for ITK (e.g.,
ITKExtras.py) that help with using ITK from numpy, accessing spacing
information, etc. I wonder if something similar should be done in this
module for MONAI.
> 2) MONAI is using python dictionaries for managing spacing etc. Seems
like those dictionaries could be created and populated by this toolkit as
well. Yes, MONAI doesn't provide a custom C++ library for those
dictionaries, but does it need to in order to access them from C++?

This may need to be implemented by adding code to ITK itself and / or customization of this module's Python interface.