Create a fake local Fitbit server

[jup014]

We might need to create a fake Fitbit server for the purpose of local development.

Features

1. It should generate realistic activity data. How do we define "realistic?" It depends... Maybe we should add a feature that pretends "non-wearing".
2. It should work with realistic authentication keys so that we can test authentication.
3. It should support a storage feature for the step goals or other stuff (what else?)
4. What else?

This is a huge job. Let's create a sub-issue if somebody has taken a step for this.

[To close this issue, you need to satisfy all of these:]

• create a docker container for it
• reroute the server Fitbit app to it (if we're local)
• implement activity data generation feature
• implement step goal storage feature
• implement auth feature
• what else? (please add more)

[jup014]

I hate this circle ;)