Development bnotions

# Approvals Required:
- [ ] @NahimNasser (Nahim)


# Stories
1. As a developer I want to support an API endpoint for retrieving the APP secret. 

# Notes
1.  Given an app-id this API endpoint returns the app-secret associated with the app id. If the app-id provided does not exist the response contains a Null app-secret. 
2. API format :  `/api/mobile/v0.5/social/app-secret/<app-id>`
3. Response format `{‘app-secret’: <app-secret>}`