Fix documentation so that developers can locally install Janssen with test data load

[ossdhaval]

The current setup instructions for Janssen needs updates:

• 'oxauth' needs to be replaced by 'jans' at many places
• Most of the steps need to be removed as they have been taken care by install.py and setup.py
• Steps mentioned in 'Prepare for tests run' can not be followed as is. They need more detailing or corrections. Same steps are marked as TODO in setup.py

Benefit: All contributing developers should be able to must run all unit tests to ensure their code is not breaking any functionality. Developer workspace to enable this should be easy to setup. A step-by-step guide will help us achieve this.

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Due: 31st May 2021