Upgrade django Oscar 1.0.2 to 2.0

[rajpaul]

We are going to upgrade django oscar from 1.0.2 to 2.0. Django Oscar 2.0 has some significant changes as well as some backward incompatible changes.

Reference Doc - https://django-oscar.readthedocs.io/en/2.1.0/releases/v2.0.html
Following this doc for code changes - https://readthedocs.org/projects/django-oscar/downloads/pdf/stable/

@natea
@mprunell

[rajpaul]

@natea I have progressed on this issue. Some internal urls i.e. catalog, checkout etc are still need to be upgraded.
And I can visit home page as well now :

[rajpaul]

@natea We have successfully upgraded django oscar from 1.x to 2.x now. Current oscar version is django-oscar 2.0. Here is the catalog - https://smallslive-staging.herokuapp.com/catalog/

There are still some issues here and there after this upgrade. I am fixing those issues on the go.