#3 Refactor followers' count to use the UserInfoResponse

TwitterManager now returns an UserInfoResponse so we can easily add new block which use the users/show api endpoints
 #3 Add default value for userInfo to avoid isset in getters
Merge pull request #17 from BenoitLeveque/refactor-twitter-follower-count-to-use-a-response-object

 #3 Refactor followers' count to use the UserInfoResponse