Add an example Django app

[DingoEatingFuzz]

To make it easier for people to learn and understand Context and context-drf, we should add an example app.

The ideal example app has the following:

1. A real database running in a docker container and automatically populated via a script and multiple CSV/JSON files checked into source control.
2. Context files for each data source.
3. Models that exercise 0, 1, and N data sources.
4. A custom view to show how to interface with the Context data sources without using mixins.

I have been using the PDX Scooter Pilot findings data as an example, since it's a good size and relevant.

Page: https://www.portlandoregon.gov/transportation/78431
Direct download: https://www.portlandoregon.gov/transportation/article/709734