feature refactorings to use UserFactory
disables Join button when hangout is not live
code review: changing host to user for Hangout
removing default Desc scope for Hangout
code review: refactor HangoutPresenter extract a private method
code review: refactore user_avatar partial
code review: refactored NullUser and UserPresenter
code review: switched to strong params in hangout.update
code review: minor refactorings in index view