Add gunicorn configuration, fix docs for docker setup

[inovizz]

There is an effort going on to dockerize junction #749, though it only covers basic docker setup, and doesn't fix docs or use gunicorn for app deployment which will be needed for actual deployment when Junction is supposed to go live.

So I am creating this issue to raise a PR against #749 to add gunicorn and fix the docs setup using docker.

P.S. - In the meantime, if PR #749 gets merged then we should refer to branch feature/upgrade-junction as current fixes w.r.t python upgrade, dockerization and other chores are gradually moving to this branch and once its settled and major items are fixed we'll merge feature/upgrade-junction to master.

Feel free to start discussions here to ask more questions.