Stub out User Followers API
Implement the User Followers API

Update comments with links to API documentation
Remove API methods that were invalid
Refactor User Followers Client

Create ApiUrls methods for base Uri's
Add unit tests
Stub out observable User Followers API
Implement Observable User Followers API

Fix up Code Analysis errors
Add unit tests for the observable client
Add integration tests
Rename UserFollowersClient to FollowersClient