Set DEBUG to False by default in all API repos

[MikeTheCanuck]

Per agreement here: https://github.com/hackoregon/civic-devops/issues/103#issuecomment-390426650

We need to turn off Debug in production, which will require setting it to False in settings.py for each project:

• [x] disaster-resilience-backend
• [x] elections-2018-backend
• [x] housing-2018
• [x] neighborhoods-2018
• [x] transportation-systems-backend-2018

This will also likely require us to toggle it to True in the env.sample or equivalent file in each project, and to notify the project owners that they need to inform their developers to toggle this in their .env files.

[MikeTheCanuck]

Fixed in all projects, and confirmed DEBUG=True is included in all env.sample and similar files.