our app fully shadows cybercoach user
* at signup we create a cybercoach user from then on
  we do not update the user in cybercoach, changes stay
  in our app. we only keep in our app a reference of cybercoach user
  trough username and password
user gets subscribed to sport 'running' on signup
* handling cybercoach and other errors on signup
* refactoring RegistrationsController and User
Merge pull request #20 from New-York-Falcons/subscribe-user-to-running

subscribe user to running & cybercoach service related user improvements