feat(dotenv): add django-dotenv support.

manage.py do not read `.env`. Let's fix that.

Usecase:
While working b/w different project it's becomes difficult to work
with environment variables. Also we don't want to track the local
enviroment varibale.

Solution:
Using django-dotenv[1], we can save all the local environment per
project in a .env file. This file should not be tracked, instead
a `.env.sample` should be used to educated the user for possible
environment variables.

[1] https://github.com/jacobian/django-dotenv