Fitbit Subscription API

[jzhou59]

Integrate Fitbit subscription API into RADAR-PushEndpoint.
Mainly modules:

• Create subscriptions for users to receive notifications.
• Create a service to receive notifications and store them(actually the offset of scope) in Redis.
• Create a processor to retrieve data from Fitbit in a real-time way.

[yatharthranjan]

I think you can change the base to dev

[yatharthranjan]

Just elaborating on the things to be done:

1. Test data received directly from fitbit and successful upload to kafka (also check redis impl is working as expected)
2. Extracting common code between rest-connector and push-endpoint to libraries so can be reused. This would include code for requests and routes primarily.
3. Documentation of the code and also in the README (to add how to use the fitbit subscription including configuration on fitbit portal)

Number 2 can be tackled later by adding a github issue for it.